Patent Application
20130141958
The field of application of the present invention is electrical energy generating systems by means of variable resource renewable energies, and more specifically, by means of wind or solar photovoltaic energy.
The object of the invention is to provide an energy management system for variable resource electrical generating systems, which incorporates means for the storing of energy and the management thereof. The system permits the needs which arise in the power grid to be met, and participates in the regulation of the power grid and contributing to the stability and quality thereof.
Within the field of electrical energy generation, conventional generating plants such as thermal or nuclear have means to, by demand of the operator of the power grid, increase or decrease the energy transmitted to the grid depending on the requirements of the power grid at each moment. In recent years, said requirements demanded by the operator of the grid are being extended to variable resource energy generating systems.
Herein, variable resource energy generating systems shall be those generating systems which are characterised by a wide variability in energetic resources. Normally, the variable resource is some type of uncontrollable renewable energy, such as the wind or the sun in systems based on wind or solar power.
The massive integration of renewable energies in the grid requires that the generation fits the demand at all times in order for correct operation thereof.
In order to resolve this problem, a first known solution against the excess of energetic resource is to limit the energy produced by the system. Nevertheless, this method implies moving the system further away from the optimal operation point to decrease the capacity thereof to capture energy, which means that a part of the energetic resource is no longer used and cannot be recovered later.
Another known solution consists of using storage means capable of consuming active power during the periods when there is an excess of energetic resource and return the stored energy to the grid when an energetic resource deficit is produced. This technique also permits a response against active power variation demands by the grid operators or acts in a coordinated manner against frequency variations which require the generation and the energy consumption to be balanced by carrying out primary and secondary regulation functions.
EP2101392 and EP1772939 disclose systems which comprise batteries or other storage means and a bidirectional DC/DC converter which permits the channelling of the excess energy towards said storage means and returns said energy to the DC bus when it is needed. However, these systems present the drawback that to manage 100% of the energy produced DC/DC converters are required of the all of the power of the system. This is often excessively expensive, in addition to increasing the total volume of the system.
The present invention discloses a system and method of energy management for the connection of a DC voltage source to the power grid. Herein, the term “DC voltage source” refers to a DC voltage source supplied from a variable renewable energy resource, such as, for example, solar photovoltaic energy, wind power, or others. Some examples of DC voltage sources are:
The energy management system proposed herein for connecting DC voltage sources to the grid includes:
A second aspect of the invention relates to a method of energy management using the described system which permits controlling the power flow exchanged with the grid through a suitable management of the energy flow between the DC source, the storage means and the grid by means of actuations on the DC/AC converter, the DC/DC converter, the additional switching element and/or the DC voltage source.
An important advantage of the disclosed system is that, by providing an alternative route to the DC/DC converter for the input or output energy of the storage means, it is possible to dimension said DC/DC converter for powers less than the maximum power of the DC source. Thus, when the power exceeds the maximum power of the DC/DC converter, the storage means charges/discharges via the additional switching element. A DC/DC converter dimensioned for lower powers is less voluminous and lighter, thus facilitating the transportation and assembly tasks, and furthermore, it is economically cheaper.
Additionally, in case of a sag of the renewable energetic resource, other conventional sources (such as thermal, combined cycle, hydroelectric, etc.) can act by participating in the secondary regulation. Nevertheless, these sources have slower dynamic power variations than those which can be featured by renewable energy origins which incorporate the system proposed in the present invention.
Therefore, the invention permits the necessary/required adjustments to be made to avoid the drawbacks characteristic of each renewable source such as:
Another important advantage of the invention is that it permits a response to the following power requirements:
The proposed invention achieves the previous objectives by means of different kinds of energy management depending on the requirement.
In periods in which the energetic resource available is greater than that required a suitable management of the converters and the additional switching element permits the charging of the storage means to be carried out according to two alternative operational modes: through the DC/DC converter or through the additional switching element. Below, these charging modes are briefly described according to a preferred embodiment:
This type of charging permits the DC source and the storage means to work at a different voltage, so that the DC source can work at the voltage corresponding to the maximum power point while the excess energy is stored in the storage means at a lower voltage.
Alternatively, at moments when the energy required is greater than that supplied by the energetic resource, a suitable management of the converters and the additional switching element permits energy to be released from the storage means towards the grid according to two modes of alternative operation. Below, these two discharging modes are briefly described according to a preferred embodiment:
In a preferred embodiment, the proposed invention permits a control of the active power generated by the system. The control of said power is performed based on orders which can be defined by the grid operator or the supervising controller of the system or the control unit or internally according to tables, parameters, etc. The orders of the grid operator can be sent to the control unit of each individual facility through a general controller of the facility. The order can also be based on power variations according to ramps, or a profile which permits a response to be given to the rest of the generating sources of the grid system.
Additionally, the system proposed herein can counteract power variations of the variable resource by adapting the output of the system to the dynamics required by the rest of the generating sources of the grid system. In the event of a sag of the renewable energetic resource, other conventional sources (such as thermal, combined cycle, hydroelectric, etc.) can act by participating in the secondary regulation. Nevertheless, these sources have slower dynamic power variations than those which can be featured by the variable resources. For example, conventional energy sources have dynamic power variations of around 4% per minute, while the dynamics of the variable resource generating systems can reach 80% in a few seconds. In the event of a sag of the variable resource greater than that which can counteract the conventional sources, the system proposed herein would supply the required difference with the response dynamic demanded.
In a preferred embodiment of the invention, the charging of the storage means could be performed by supplying the system from the grid via the AC/DC converter. This permits the storage means to act as controlled charge with an energy balance of the facility negative or lower than that established by the DC voltage source.
In the case of facilities formed by several generation units, the storage solution can be found in each generation unit or in the facility, for example at the output of the system. The present invention suggests the storage considering each individual facility (instead of all of the facilities), so that the use of the energetic resource is optimised.
The voltage of the storage means is selected so that it is less than the nominal value of the DC source and greater than the minimum operational voltage required by the DC/AC converter, in accordance with the grid voltage and the topology thereof.
Below, in order to facilitate a better understanding of this specification and forming an integral part thereof, attached are figures wherein, in an illustrative and non-limitative manner, the object of the invention has been represented.
The system proposed herein is characterised in that at least one control unit controls the output power of the system (1), managing the energy flow between the DC source (5), the storage means (4) and the grid (7), acting on the DC/AC converter (6), the DC/DC converter (2) and the first branch formed by a switching element (3, 3′) and/or the DC voltage source (5).
Below are described the different modes of operation of this system (1). In the first place, in periods during which the energetic resource is greater than that required, the system (1) permits the storage means (4) to be charged in two different ways:
In a preferred embodiment of the invention, the charging of the storage means (4) can be performed by supplying the storage means (4) from the grid (7) via the AC/DC converter (6). This permits the storage means (4) to act as controlled load with an energy balance of the facility negative or lower than that established by the DC voltage source (5).
On the other hand, at moments when the energy required by the grid (7) is greater than that supplied by the energetic resource, energy is discharged from the storage means (4) towards the grid (7). There are two modes of discharge:
The minimum operating voltage shall be determined by the application or origin of the energetic resource. In the case of wind powered applications, the minimum operating voltage shall be that such that it functions within the safety limits, so that both the grid (7) voltage and that imposed by the electrical machine must be taken into account. This voltage, whether it is that of a rotor in double-feed topologies, or that of a stator, in full converter topologies, is in turn imposed by the rotational velocity.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/ES10/70546 | 8/11/2010 | WO | 00 | 2/11/2013 |
