ELECTRICAL SYSTEM TO STABILIZE THE VOLTAGE FOR CONVEYANCE TO THE GRID IN WIND AND PHOTOVOLTAIC GENERATION FACILITIES

Abstract

An electrical system for stabilizing the grid evacuation voltage in wind and photovoltaic power generation installations, characterized in that a synchronous motor and generator assembly is interposed between the frequency inverters and the step-up transformer.

Description

ELECTRICAL SYSTEM TO STABILIZE THE EVACUATION VOLTAGE TO NETWORK IN WIND AND PHOTOVOLTAIC GENERATION FACILITIES TECHNICAL SECTOR The present invention belongs to the energy field and in particular to the generation of electrical energy, focusing on optimizing the quality of the electricity supply and the response of wind and photovoltaic generation facilities to network disturbances. BACKGROUND OF THE INVENTION The electricity generation sector has undergone a major transformation in the last decade, driven by the global transition to sustainable energy sources to replace fossil fuel-based power generation. This evolution, combining widely distributed and intermittent renewable energy generation with the phase-out of fossil fuel-based generation facilities, presents a significant challenge for electricity grid operators, who must ensure stable, reliable, and secure energy transmission and distribution.The aforementioned concept of challenge refers to the fact that some renewable energy generating plants, such as photovoltaic and wind farms, deliver less stable electricity to the grid in terms of their response to potential system disturbances, compared to conventional hydroelectric, nuclear, or combined cycle power plants. In the face of such disturbances, the former have virtually no responsiveness, while the latter have an adequate damping capacity. In an electrical system, there must be a continuous balance between electricity generation and consumption, with the grid frequency being the indicator of this balance.When large imbalances occur, qualities such as the frequency or voltage of the network can be affected, so that if large variations occur in generation or consumption, for example, when a generating installation operating at full load is disconnected from the network instantaneously, there must be sufficient inertia in the electrical network to attenuate or avoid any unwanted effect. One of the main differences between conventional and renewable technologies, which is directly related to the aforementioned problem, lies in the fact that conventional technologies use synchronous generators. These generators provide electrical power with adequate stability in terms of frequency and voltage level in their output waveform. Furthermore, the Spanish electrical system is designed to receive electricity from conventional power plants because these were the types of plants that existed when the system was designed. Therefore, it is necessary to investigate how to adapt the recent wind and photovoltaic technologies, which are also experiencing constant growth due to their significant advantages based on harnessing the resources of the sun and wind, both renewable and inexhaustible sources. Technologies exist for improving the output signal of photovoltaic and wind power generating installations, with configurations and arrangements different from that presented in this invention. References to prior applications are cited below: 1. SYSTEM FOR GENERATION OF CONSTANT FREQUENCY ELECTRICAL POWER FROM WIND ENERGY. Publication number ES 2056 732 (01.10.1994). Applicant: DOMINGO HUARTE FRANCÉS AND LAURA HUARTE RICO. 2. MAGNETICALLY COUPLED FLYWHEEL. Publication number ES2901007 T3 (21.03.2022). Applicant: CHAKRATEC LTD. 3. SYNCHRONOUS POWER CONTROLLER FOR A GENERATION SYSTEM BASED ON STATIC POWER CONVERTERS. Publication number 2 402467 (03.05.2013). Applicant: ABENGOA SOLAR NEW TECHNOLOGIES SA 4. SYNCHRONOUS CONTROL METHOD FOR PLANTS WITH MULTIPLE DISTRIBUTED POWER GENERATION UNITS. Publication number 2 816798 (05.04.2021). Applicant: UNIVERSITAT POLITÉCNICA DE CATALUNYA. 5. SYNCHRONOUS GENERATOR. Publication number ES2292497 T3 (16.03.2008). Applicant: WOBBEN, ALOYS. 6. SYNCHRONOUS GENERATOR FOR WIND TURBINES. Publication number ES2656821 A1 (28.02.2018). Applicant: SIEMENS GAMESA RENEWABLE ENERGY INNOVATION & TECHNOLOGY, SL EXPLANATION OF THE INVENTION The system proposed in this invention is based on a novel configuration consisting primarily of an electric motor that powers a synchronous generator, thus enabling the integration and application of the advantages of the synchronous generator to wind and photovoltaic renewable energy technologies. Therefore, this innovation represents a significant improvement in the aforementioned research area, as it allows for the control of the power supplied to the grid by a renewable energy source.Furthermore, it is possible to directly control voltage and frequency parameters to correct deviations produced either within the generation plant itself or externally, contributing to the dynamic stability of the network as well as frequency regulation, thanks to the control of both active and reactive power. This ensures that the entire renewable generation plant (wind or photovoltaic), when incorporating this new electrical system, behaves the same as a conventional generation installation in terms of dynamic stability in the face of fluctuations in the network. The location for incorporating the new system, consisting mainly of an electric motor and a synchronous generator, is indicated below according to the field of application: - In application to photovoltaic solar plants: an electrical power generation system (solar field with photovoltaic panels), an electronic power inverter to convert direct current electrical energy to alternating current at the grid frequency, the designed set of synchronous motor-generator mechanically coupled to each other and the evacuation position for supplying the generated energy to the grid. - For wind farm applications: an electrical power generation system (wind turbine with gearbox and asynchronous generator), an electronic power rectifier-inverter assembly to convert alternating current to direct current and then back to alternating current at grid frequency. The new configuration of mechanically coupled synchronous motor-generator is then inserted, and the output continues to the grid for supplying the generated energy to the grid. The competitive advantages offered by the proposed new synchronous motor-generator system include, among others: - Improved frequency stability, by having a moving mass, the mechanically coupled synchronous motor and generator assembly form a flywheel and inertia, that is, a large mass in uniform rotary motion, which allows for an instantaneous injection of active power in the event of a fault in the network, whether due to overload of the network due to the loss of instantaneous generation that generates an underfrequency or the loss of instantaneous load due to an instantaneous disconnection of a high load that generates an overfrequency in the network. - Improved voltage stability, by providing instantaneous response capacity to network disturbances in the event of a short-circuit fault, contributing: During a short circuit, a short-circuit current value provides several kA that contribute to the fault and allow the electrical protection equipment to clear the fault more quickly, thanks to the subtransient reactance (Xd) that allows a large instantaneous contribution of reactive power. · After the short circuit, through a rapid supply of reactive power after the fault is cleared, thanks to the transient reactance of the synchronous generator (Xd) and a rapid regulation of the excitation system of the synchronous generator. - Improved reactive power regulation under normal operating conditions, adjusting the reactive power generated by the generator to achieve precise voltage adjustment: · By increasing the generation of reactive (+Q) or inductive power, an increase in the voltage of the synchronous generator is achieved. · By decreasing the generation of reactive (-Q) or capacitive power, a decrease in the voltage at the output of the synchronous generator is achieved. - Elimination in the power transformers of the evacuation substations of wind farms and photovoltaic plants of the on-load regulation systems of the transformers and auxiliary equipment (Jansen relay), since this function is performed more quickly and accurately with the reactive power regulation in the synchronous generator. BRIEF DESCRIPTION OF THE DRAWINGS To complement the description being made and in order to help a better understanding of the characteristics of the invention, a set of drawings is included as an integral part of said description, in which, for illustrative and non-limiting purposes, the following has been represented: Figures 1a and 1b show the simplified single-line diagram of photovoltaic generating installations. Figure 1a represents a typical photovoltaic generating installation currently in existence, and Figure 1b represents a typical photovoltaic generating installation with the present invention incorporated. Figures 2a and 2b show the simplified single-line diagram of wind generating installations. Figure 2a represents a typical wind turbine installation currently in existence, and Figure 2b shows the typical photovoltaic generating installation with the proposed invention incorporated. PREFERRED EMBODIMENT OF THE INVENTION In this text, the term "understands" and its derivatives (such as "understanding", etc.) should not be understood in an exclusive sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include more elements, stages, etc. Two new preferred embodiments of the invention are presented below, based on the energy source technology: solar photovoltaic and wind. The various elements comprising the simplified single-line diagram shown in Figure 1b are presented descriptively. This diagram illustrates a photovoltaic plant with the proposed new layout, which includes, as additional elements to the existing typology (Figure 1a), a three-phase motor and a synchronous generator, along with the auxiliary equipment necessary for their proper operation in this new configuration. The proposed new photovoltaic plant layout is comprised, in an illustrative and non-exhaustive manner, of the following main elements, listed in ascending order as shown in Figure 1b: - Photovoltaic modules: are grouped in series according to the assigned nominal voltage, forming direct current lines, such that they all have the same voltage level. - String box: these group the direct current lines coming from the photovoltaic modules, each of which has a disconnect switch with cutting power for maintenance work and a fuse to protect against overcurrent. - DC power lines: main lines that evacuate the energy from the different string boxes to the inverter. - Step-up inverter: converts direct current (DC) electrical energy to alternating current (AC). It consists of switches 52-1, 52-2, and 52-3, the inverter module (the main power electronics unit containing several power modules operating in parallel, the number of which is scalable depending on the plant's installed power), and the step-up transformer, which increases the AC voltage generated at the inverter's output from between 1,000 V and 3,000 V to a higher voltage for transmission within the plant (15,000-20,000 V). - AC evacuation lines: originating from each of the transformer substations and inverters of the photovoltaic installation, these lines converge at a circuit breaker (52-M) to operate the plant's three-phase power motor. - Three-phase power motor: indicated in Figure 1b as (M 3~), through which the electrical energy generated in alternating current by all the inverters of the photovoltaic plant is transformed into rotary motion. The purpose of this motor is to provide physical inertia to the installation, as it has a large moving mass (rotor) that will behave as a large flywheel together with the three-phase generator. The motor has the following auxiliary components: or Associated electrical equipment: (voltage transformers and current transformers) that monitors the magnitudes of the electrical energy supplied from the inverters to the motor and sends these magnitudes in reduced values ​​to the electrical protections. or Motor electrical protections: it has overvoltage, overcurrent, differential motor function and phase imbalance functions. o Auxiliary cooling system: allows the evacuation of excess temperature generated by the operation of the engine. Process instrumentation and control: This refers to the set of instruments installed on the engine and its auxiliary equipment for monitoring and ensuring its proper operation. These instruments, while not exhaustive, include: temperature sensors, pressure switches, flow meters, level sensors, voltmeters, ammeters, wattmeters, and tachometers. These instruments transmit parameters to the control system (SCADA) for the correct operation of the system. - Three-phase synchronous generator: indicated in Figure 1b as (G 3~), driven via a transmission shaft by the three-phase power motor, it generates alternating current with the capacity to regulate the generator's output voltage through a direct-excited automatic voltage regulator (AVR) with a PID loop. This regulator takes the reference AC voltage from the generator's output and, via an external thyristor bridge, controls the DC voltage applied to the generator's rotor, with the same arrangement and operating logic as conventional power plants such as hydroelectric, combined cycle, and nuclear. Like the motor, the synchronous generator provides synchronous inertia for stabilizing the grid voltage in the event of disturbances, as described in the Explanation of the Invention section. The generator has the following auxiliary elements: or Associated electrical switchgear (voltage transformers and current transformers) that monitor the magnitudes of the electrical energy generated through the transformation of the rotary mechanical energy of the motor and send these magnitudes in reduced values ​​to the electrical protections. or Generator electrical protections: it has at least the following protection functions: Protection against overvoltages and undervoltages. Protection against overfrequency and underfrequency. Generator differential. Protection against phase imbalance. o Auxiliary cooling system: allows the evacuation of excess temperature generated by the operation of the generator. Instrumentation and associated process control: This refers to the set of instruments installed on the engine and its auxiliary equipment for monitoring and ensuring its proper operation. These instruments, while not exhaustive, include: temperature sensors, pressure switches, flow meters, level sensors, voltmeters, ammeters, wattmeters, and tachometers. These instruments transmit parameters to the control system (SCADA) for the correct operation of the system. - Power transformer: This increases the generation voltage for transmission to the grid. In this case, it does not have on-load tap changer regulation, as this function is performed by the automatic voltage regulator of the synchronous generator. It has circuit breakers on the low-voltage side of the transformer (circuit breaker 52-BT) to electrically isolate and protect the generator from the transformer. On the high-voltage side, the transformer has surge protection devices (surge protectors) against potential overvoltages from outside the grid. - PASS or 'plug and switch' type module, a single set of operating and protection elements that combine the following functions into a single piece of equipment: or Transformer isolation switch: 89-A. or Grounding switch PaT next to the power transformer: 57-1. or Automatic switch 52-AT, through which the synchronous generator is coupled to the network, by means of telecontrol equipment and through a network synchronizer. o Line disconnector: 89-L. or PaT disconnector next to the circuit breaker: 57-2. A second preferred embodiment of the invention is presented below, detailing the various elements comprising the simplified single-line diagram shown in Figure 2b. This diagram illustrates a wind farm with the proposed new arrangement, which includes, in addition to the existing typology (Figure 2a), the three-phase motor and synchronous generator, along with auxiliary equipment. The new wind power generation installation is comprised, in an illustrative and non-limiting manner, of the following main elements, listed in ascending order as shown in Figure 2b: - Wind turbine: mainly composed of the following elements: Wind turbine: consisting of blades and a blade pitch control system. Transmission system: includes the slow shaft that transfers the motion from the turbine, the gearbox system, and the fast shaft. o Generator: receives the torque from the high-speed shaft and transforms the mechanical energy o Electronic converters: from alternating current to direct current and from direct current to alternating current o Step-up transformer to medium voltage: to increase the output voltage, usually around 690 V to the transmission voltage for the wind farm 10-20 kV, it has switches on both sides of the transformer 52-2 and 52-3.- Alternating evacuation lines: coming from each of the wind turbines of the photovoltaic installation, converge at an automatic switch for the operation of the plant's three-phase power motor (52-M). - Three-phase power motor: indicated in Figure 2b as (M 3~), through which the electrical energy generated in alternating current is transformed in all the wind turbines of the wind farm. The purpose of this motor is to provide physical inertia to the installation, as it has a large moving mass (rotor) that will behave as a large flywheel together with the three-phase generator. The motor has the following auxiliary elements: or Associated electrical equipment (voltage transformers and current transformers) that monitor the magnitudes of the electrical energy supplied from the inverters to the motor and send these magnitudes in reduced values ​​to the electrical protections. or Motor electrical protections: it has overvoltage, overcurrent, differential motor function and phase imbalance functions. o Auxiliary cooling system: allows the evacuation of excess temperature generated by the operation of the engine. Instrumentation and associated process control: This refers to the set of instruments installed on the engine and its auxiliary equipment for monitoring and ensuring its proper operation. These instruments, while not exhaustive, include: temperature sensors, pressure switches, flow meters, level sensors, voltmeters, ammeters, wattmeters, and tachometers. These instruments transmit parameters to the control system (SCADA) for the correct operation of the system. - Three-phase synchronous generator: indicated in Figure 2b as (G 3~), driven via a transmission shaft by the three-phase power motor, will generate an alternating current capable of regulating the generator's output voltage through a direct-excited automatic voltage regulator (AVR) with a PID loop. This regulator takes the reference AC voltage from the generator's output and, via an external thyristor bridge, controls the DC voltage applied to the generator's rotor, with the same arrangement and operating logic as conventional power plants such as hydroelectric, combined cycle, and nuclear plants. Like the motor, the synchronous generator provides synchronous inertia for stabilizing the grid voltage in the event of disturbances, as described in the Explanation of the Invention section. The generator has the following auxiliary elements: or Associated electrical switchgear (voltage transformers and current transformers) that monitor the magnitudes of the electrical energy generated through the transformation of the rotary mechanical energy of the motor and send these magnitudes in reduced values ​​to the electrical protections. or Generator electrical protections: it has at least the following protection functions: Protection against overvoltages and undervoltages. Protection against overfrequency and underfrequency. Generator differential. Protection against phase imbalance. o Auxiliary cooling system: allows the evacuation of excess temperature generated by the operation of the generator. Instrumentation and associated process control: This refers to the set of instruments installed on the engine and its auxiliary equipment for monitoring and ensuring its proper operation. These instruments, while not exhaustive, include: temperature sensors, pressure switches, flow meters, level sensors, voltmeters, ammeters, wattmeters, and tachometers. These instruments transmit parameters to the control system (SCADA) for the correct operation of the system. - Power transformer: This increases the generation voltage for transmission to the grid. In this case, it does not have on-load tap changer regulation, as this function is performed by the automatic voltage regulator of the synchronous generator. It has circuit breakers on the low-voltage side of the transformer (circuit breaker 52-BT) to electrically isolate and protect the generator from the transformer. On the high-voltage side, the transformer has surge protection devices (surge protectors) against potential overvoltages from outside the grid. - PASS or 'plug and switch' type module, a single set of operating and protection elements that combine the following functions into a single piece of equipment: or Transformer isolation switch: 89-A. or PaT disconnector next to the power transformer: 57-1. or Automatic switch 52-AT, through which the synchronous generator is connected to the network, by means of telecontrol equipment and through a network synchronizer. o Line disconnector: 89-L. or PaT disconnector next to the circuit breaker: 57-2. The invention is industrially applicable, as the additional components required are already available on the market and are therefore easily adaptable and transferable to this new configuration. However, the method of powering the synchronous generator via the electric motor, which must be connected beforehand, is inventive. Furthermore, various auxiliary and protective devices, in accordance with applicable regional regulations, are required for the new assembly to function properly and meet the new and necessary functionalities in the renewable energy sector.

Claims

1. An electrical system for stabilizing the grid evacuation voltage in wind and photovoltaic power generation installations, characterized in that a synchronous motor and generator assembly is interposed between the frequency inverters and the step-up transformer.

2. An electrical system for stabilizing the grid evacuation voltage in wind and photovoltaic power generation installations, comprising an electric motor and synchronous generator assembly according to claim 1; in the case of a photovoltaic plant, the assembly is interposed between the inverter and the power transformer.

3. An electrical system for stabilizing the grid evacuation voltage in wind and photovoltaic power generation installations, comprising an electric motor and synchronous generator assembly according to claim 1; in the case of a wind power generation installation, the assembly is interposed between the wind turbines and the power transformer. 4.Electrical system for stabilizing the grid connection voltage in wind and photovoltaic power generation installations, comprising an electric motor and synchronous generator assembly according to claim 1, characterized in that it contains auxiliary equipment and protection elements, both upstream of the electric motor and at the output of the synchronous generator.

5. Electrical system for stabilizing the grid connection voltage in wind and photovoltaic power generation installations, characterized in that the power generated by the plant is subdivided among several synchronous motor-generator assemblies of identical characteristics connected in parallel.