WO2016133467A1

WO2016133467A1 - A photovoltaic system for controling single phase photovoltaic sources for optimal self-consumption

Info

Publication number: WO2016133467A1
Application number: PCT/SI2015/000009
Authority: WO
Inventors: Jurij STANGL; Jurij VIDALI
Original assignee: Amk D.O.O., Inzeniring, Svetovanje, Trgovina; Teletel A, Informacijske Storitve, D.O.O.
Priority date: 2015-02-20
Filing date: 2015-02-20
Publication date: 2016-08-25

Abstract

The present invention is a photovoltaic system, which with its structure and integrated algorithms enables optimal self-consumption of electrical energy. The system structure, with one or more photovoltaic sources (13-1, 13-2, 13-3), one or more micro-inverters (12-1, 12-2, 12-3) equipped with solid-state relay switches, controllable consumer loads (15-1, 15-2, 15-3) and non-controllable electric consumer loads (16-1, 16-2, 16-3), and a measuring and control device (8) with an integrated control algorithm, forms a base for achieving an optimal self-consumption of electrical energy, minimizing the impact of asymmetrical load on the multi-phase AC power grid and enabling consumer load management in accordance with user requirements in one unified system.

Description

A PHOTOVOLTAIC SYSTEM FOR CONTROLING SINGLE PHOTOVOLTAIC SOURCES FOR OPTIMAL SELF-CONSUMPTION

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a photovoltaic system, which comprises one or more single-phase photovoltaic sources, one or more micro-inverter units with solid-state relay switches, a measurement and control device with an integrated algorithm, to be used for optimization of electrical energy usage. The present invention belongs to the field of electricity, more precisely to the field of generation, conversion, or distribution of electric power.

BACKGROUND OF THE INVENTION AND THE TECHNICAL PROBLEM

It is well known that single-phase consumer loads are distributed over individual phases of a multi-phase AC power grid, cause internal grid asymmetry in taking electrical energy for a plurality of consumer loads out of a multi-phase AC power grid. The internal grid asymmetry should be compensated to minimize the impact on the multi-phase AC power grid. Undesired asymmetrical energy distribution also occurs in a single-phase feeding electric energy into a multi-phase AC power grid.

The technical problem is how to create a photovoltaic system, which would be capable to achieve an optimum for self-consumption of electrical energy or different predefined goals with the implementation of different control algorithms. The solution has to incorporate a combination of units and/or devices, which are capable to control the electric energy flow from single-phase photovoltaic sources to a particular individual phase conductor, in order to measure differences in the flow and value of electrical energy in the individual phase conductors and control controllable consumer loads at the same unit of time. The case of an extreme unbalanced load due to taking energy at the grid connection point via one phase while simultaneously feeding energy into the AC power grid via another phase is a disadvantage independent of the unbalanced load provoked in the AC power grid, if self-consumption of the electric energy is advantageous. These advantages generally include that self-consumption of a locally generated electric energy does not load the AC power grid.

Additional financial advantages may occur, if the electric energy taken from the AC power grid is more expensive than the electric energy generated locally and fed into the AC power grid. A financial advantage may also occur if an incentive for self-consumption of locally generated electric energy is higher than the difference between the payment for the electric energy fed into the grid and the price of electric energy taken from the grid. This is the case in many countries where net- metering scheme is presented. The maximization of the self-consumption has financial advantages in countries, in which the price of electric energy, together with the net usage fee and other taxes, taken from the grid is higher than the price of locally generated energy.

STATE OF THE ART

From DE 10 2006 003 it is known to counter-act these asymmetries so that electric energy fed by a plurality of single phase inverters into an AC power grid are evenly distributed over the phases of the AC power grid and that upon breakdown of one inverter feeding into one phase, the powers of the other inverters feeding in other phases are limited.

Document US 4, 177,508 discloses an apparatus for use in balancing an asymmetrical load, which is supplied from a three-phase network. The apparatus is provided with an inverter for generating a three-phase output current system on its AC side, which is fed with phases reversed to the network. The DC side of the inverter, in turn, is fed from a DC source with a DC current corresponding to the maximum asymmetry power to be balanced. Preferably, the DC source is a rectifier connected to the network. Thus, the entire known apparatus is only provided for balancing the asymmetrical load, resulting in considerable costs and power losses.

Document WO 201 1 089 181 A1 discloses an apparatus and an inverter for leveling partial powers at a grid connection point between a multi-phase AC power grid comprising a plurality of phase conductors, on the one hand, and a unit including a multi-phase inverter, which feeds electric energy into the AC power grid, plus consumer loads connected to the AC power grid, on the other hand, the partial powers flowing via the individual phase conductors, by which a self- consumption of locally generated power is optimized and by which asymmetrical loads on a multi-phase AC power grid at the grid connection point are reduced in general. Thus, the entire known apparatus and the inverter are not capable to use all possibilities of maximizing the self-consumption.

Document WO 2012 136 836 A1 discloses a method for optimizing a time course of electric power consumption by a diverse group of consumers with regard to a range of electric power, the electric power of at least one wind or solar power generator and power includes the bi-directional with a precious memory is exchanged for electrical energy and/or a public power grid, an electric power consumption is first measured in order to determine characteristic time courses of consumption of electric power by the individual consumer. Then a forecast for the timing of the supply of electric power from the at least one generator for a future point in time is created. The method is complicated, built with a battery storage, which eventually means higher investment cost. It is less flexible than the present invention, and only provides controllable loads, but not controllable photovoltaic sources, as is the case in the present invention. There is a strong interest and a growing need for a photovoltaic system, which will be capable to measure the difference in flow and value of electrical energy, to control a single phase photovoltaic sources and controllable consumer loads for optimal self-consumption at the exact same time, causing compensation of partial flow of electrical energy at grid connection point between a multi-phase AC power grid, comprising a plurality of phase conductors, and micro-inverter units, which feed electric energy in to the corresponding individual phase conductors, plus controllable and non-controllable consumer loads connected to the AC power grid, in order to maximize self-consumption.

SUMMARY OF THE INVENTION

The essence of the present invention is that the photovoltaic system comprises one or more photovoltaic sources, one or more micro-inverter units with a solid- state relay switch (SSR), a measurement and control device with an integrated control algorithm, and that the system is able to monitor and measure the difference in electrical energy flow and value, control single-phase photovoltaic sources and consumer loads in order to optimize self-consumption in the exact same time, causing compensation of partial flows of electrical energy at grid connection point, between a multi-phase AC power grid, comprising a plurality of phase conductors and a sum of single phase controllable and non-controllable consumer loads.

The measurement and control device measures and causes regulation of partial flow of electrical energy at grid connection point between a multi-phase AC power grid and internal AC power grid.

The micro-inverter unit with the solid-state relay switch (SSR) switches the flow of electrical energy into the individual phase conductor according to detected differences between the partial flow and value of electrical energy via individual phase conductors using the algorithm to reduce and compensate the determined differences. Other functions and advantages of the invention will become apparent to anyone with electro technical skill in the art upon examination of the following drawings and the detailed description. It is intended that all other additional functions and advantages, shall be included within the scope of the present invention, as defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described in more detail with reference to the drawings. The components in the drawings are not necessary to scale, emphasis is instead being placed upon clearly illustrating the present invention principles.

Fig. 1 illustrates the photovoltaic system, which in a first embodiment includes the micro-inverter unit with a solid-state relay switch and the measurement and control device with self-consumption optimization algorithms. Fig. 2 illustrates one of the implications of the algorithm in the measurement and control device, for the real case scenario.

DESCRIPTION OF THE INVENTION

The photovoltaic system according to the invention has the ability to measure the difference in the flow and value of electrical energy, to control single phase photovoltaic sources and controllable consumer loads for optimal self-consumption in the exact same time, causing compensation of partial flow of electrical energy at grid connection point between the multi-phase AC power grid, comprising a plurality of phase conductors, and micro-inverter units, which feed electric energy in to the corresponding individual phase conductors, and controllable and non- controllable consumer loads connected to the AC power grid. The photovoltaic system comprises:

- one or more photovoltaic sources,

- one or more micro-inverter units each equipped with a solid-state relay switch, which switches the flow of electrical energy into the individual phase conductor, - the measurement and control device, which detects differences between the partial flow and value of electrical energy via the individual phase conductors and using an algorithm consequently causes reduction and compensation of differences determined by feeding different partial flow of electrical energy into individual phase conductors and controls controllable consumer loads in the exact same time, with the aim of optimizing self-consumption.

The measurement and control device according to the invention, measures the flow and value of energy in the individual phase conductors at the unit of time. Based on the measurement and the integrated algorithm the control device controls photovoltaic sources and controllable consumer loads at the same unit of time. In order to achieve optimal self-consumption several parameters listed below can be used in the algorithm alone or in any combination:

- a current state of energy generation and diagnostic data for single-phase photovoltaic sources 13,

- a sum of single-phase controllable consumer loads 15, and

- additional user preferences for controllable consumer loads 15.

In order to achieve minimum impact of asymmetrical load on the multi-phase AC power grid additional specific country grid requirements may be added to the algorithm.

Furthermore, the present invention includes the micro-inverter unit with the solid- state relay switch (SSR), which is capable to switch the single-phase photovoltaic source to feed-in partial energy into the individual phase conductor for optimal self- consumption, cause compensation of electrical energy partial flow. Micro-inverter units with solid-state relay switches reduce and compensate differences by feeding different partial flows of electrical energy into the individual phase conductors when using the solid-state relay switch. It is widely known that the SSR is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals. The SSR provides many advantages that are important for micro-inverter application: a high degree of reliability, long service life, significantly reduced electromagnetic interference due to the zero-cross effect, fast response and high vibration resistance. The zero-cross effect means that if the input signal is applied at any point during the AC output wave other than very close to the zero voltage point of that wave, the output will "wait" to switch on until the AC wave reaches the following zero point. The zero-cross function puts the relay to turn ON when the AC load power supply approaches zero Volts to suppress noise generated when the load current rises suddenly. There are two types of noise: noise on power lines and noise emitted into open spaces. The zero cross function is effective against both types of noise.

The self-consumption optimum of the locally generated electric energy can be achieved by means of switching the energy fed by the photovoltaic sources to one or few phase conductors. It is sufficient to determine energy flow directions and the values through the individual phase conductors at the grid connection point. The measurement represents the state of controllable and non-controllable consumer loads at the unit of time, which is the basis for controlling the single- phase photovoltaic sources to achieve a self-consumption optimum and minimize the impact of the asymmetrical load on the multi-phase AC power grid.

Dimensioning of photovoltaic sources with regard to the partial outputs attributed to the individual phases of the AC power grid needs not to be varied as compared to the usual part of the maximum feeding energy, if, at maximum feeding energy, the locally generated electric energy exceeds the locally consumed electric energy anyway. If the sum of photovoltaic sources has a smaller dimension, it is advantageous to be able to concentrate its entire feeding energy, even with the sum of maximum feeding energy, to a single phase or phase conductor of the multi-phase AC power grid. It is an advantage, to be able to control photovoltaic sources and controllable consumer loads in the same time. We can choose only the largest consumer loads to control them for optimizing a time course of consumption of electric power as described in WO 2012 136 836 A1 . All other non-controllable consumer loads can be compensated by means of switching the energy fed by the photovoltaic sources, to the corresponding phase conductor, to achieve the self-consumption optimum.

One possible embodiment of the photovoltaic system according to the invention is shown in Fig. 1 , in which a grid connection point 7, between a three-phase AC power grid and a plurality of photovoltaic sources 13-1 , 13-2, 13-3 with micro- inverters 12-1 , 12-2, 12-3, controllable consumer loads 15-1 , 15-2, 15-3 and non- controllable electric consumer loads 16-1 , 16-2, 16-3 are depicted. The lines of the AC power grid include a zero conductor N and three phase conductors L1 , L2, L3 for the three phases of the AC power grid. The micro-inverters 12-1 , 12-2, 12-3 with solid-state relay switch 17 are feeding electrical energy generated from photovoltaic sources 13 into all three-phase conductors L1 , L2, L3. The controllable and non-controllable consumer loads 15-1 , 15-2, 15-3, 16-1 , 16-2, 16- 3 are single-phase consumer loads, which each take electric power from one phase of the AC power grid. The consumer loads 15-1 , 16-1 are connected between the phase conductor L1 and the zero conductor N, the consumer loads 15-2, 16-2 are connected between the phase conductor L2 and the zero conductor N and the consumer loads 15-3, 16-3 are connected between the phase conductor L3 and the zero conductor N. There may be more controllable or non-controllable consumer loads than depicted, connected between optional phase conductor L1 , L2, L3 and the zero conductor N. At the grid connection point 7, electric energy flows via the individual phase conductors L1 , L2, L3, particularly their energy flow directions and values, are determined by measuring and control device 8. The measuring and control device 8 may be electrical meter which phase-by-phase monitor the electric energy taken out of the AC power grid 7 and the electric energy fed therein. Voltage measurement signals 5-1 , 5-2, 5-3, 5-4 and current measurement signals 6-1 , 6-2, 6-3, 6-4 represent the state of controllable and non- controllable consumer loads at the unit of time, corresponding to energy flow directions and values at the individual phase conductors L1 , L2, L3. Corresponding algorithm in the measuring and control device 8 is controlling single-phase photovoltaic sources via operational signal 1 1 and controllable consumer loads via control signal 0 with the aim of achieving a self-consumption optimum and minimizing the impact of asymmetrical load on the multi-phase AC power grid, at the same unit of time.

In order to describe the photovoltaic system functioning Fig. 2 will be used, which shows the power distribution of controllable consumer loads 15-1 , 15-2, 15-3 and non-controllable consumer loads 16-1 , 16-2, 16-3 and photovoltaic sources 13-1 , 13-2, 13-3, at the same unit of time. The consumer loads are loading the AC power grid with 2/6 P of the load on the phase conductor L1 , 1/6 P of the load on the phase conductor L2 and 1/6 P+1/3 P=3/6 P of the load on phase conductor L3. These loads can be compensated with the corresponding switch 17 of the photovoltaic sources 13-2 from normal position on phase conductor L2 to the phase conductor L3. In this state energy flow is generated according to the new distribution of photovoltaic sources 13-1 , 13-2, 13-3, 2/6 P to the phase conductor L1 , 1/6 P to the phase conductor L2 and 3/6 P to the phase conductor L3 and achieve the state, that no electric energy would flow to/or from the AC power grid at all. The photovoltaic sources 13-1 , 13-2, 3-3 are supplying the consumer loads in the sense of a complete self-consumption of the locally generated electric energy and there is no impact of the asymmetrical load on the multi-phase AC power grid, at the same unit of time.

With the implementation of different control algorithms, predefined goals, user requirements or optimum for self-consumption of electrical energy can be achieved.

The photovoltaic system according to the invention allows optimization of electrical energy usage, minimizing the impact of asymmetrical load on the multi-phase AC power grid and enabling consumer load management in accordance with user requirements in one unified system. LIST OF REFERENCE NUMERALS L1 , L2, L3 Phase conductors

N Neutral conductor

5-1 , 5-2, 5-3, 5-4 Voltage measurement signal

6-1 , 6-2, 6-3, 6-4 Current measurement signal

7 AC power grid, grid connection point

8 Measurement and control device

9 Remote view and control

10 Control signal

1 1 Operational signal

12-1 , 12-2, 12-3 Micro-inverters

13-1 , 13-2, 13-3 Photovoltaic sources

14-1 , 14-2, 14-3 Load control switches

15-1 , 15-2, 15-3 Controllable consumer loads

16-1 , 16-2, 16-3 Non-controllable consumer loads

17 Solid-state relay switch

Claims

PATENT CLAIMS

1 . A photovoltaic system comprising at least the following components:

- one or more photovoltaic sources (13) generating electrical energy independently from a multi-phase AC power grid (7),

- one or more micro-inverter units (12) each equipped with a solid-state relay switch (17) switching and controlling single-phase photovoltaic sources (13) as well as feeding electric energy into individual phase conductors (L1 , L2, L3),

- a measurement and control device (8) with an integrated control algorithm, measuring differences in electrical energy flow and value,

said components communicate with control signals (10) and operational signals (1 1 ) in order to implement algorithm to optimize self-consumption.

2. The photovoltaic system according to claim 1 , characterized in that a current state of energy generation and diagnostic data for single-phase photovoltaic sources (13) can be used in the algorithm, in order to achieve optimal self- consumption.

3. The photovoltaic system according to claim 1 and 2, characterized in that a current state of energy generation and diagnostic data for single-phase photovoltaic sources (13) and a sum of single-phase controllable consumer loads (15) can be used in the algorithm, at the same unit of time in order to achieve optimal self-consumption.

4. The photovoltaic system according to claims 1 , 2, and 3, characterized in that additional user preferences for controllable consumer loads (15) can be used in the control algorithm in order to achieve optimal self-consumption and user requirements.

5. The photovoltaic system according to claims 1 , 2, and 3, characterized in that additional specific country grid requirements in the control algorithm can be used in order to achieve minimum impact of asymmetrical load on the multiphase AC power grid.

6. A micro-inverter unit for the system according to any of the preceding claims, characterized in that is equipped with controllable solid-state relay switch (17), which is capable to feed different partial flows of electrical energy into the individual phase conductors when using the solid-state relay switch.