RU2707084C1 - Electric power distribution and conversion device - Google Patents

Abstract

FIELD: electronic equipment.

SUBSTANCE: invention relates to converting electronic equipment and can be used in designing inverters for alternative power sources. Essence of the claimed invention consists in the fact that the complete electric power distribution and conversion device, connected by means of the input switching units with photoelectric modules (PHEM) arrays, includes a central inverter module (CIM) with a set of power cells of inverters with sine filters, a transformer whose primary winding is connected to the network through an output switching cell, wherein the number of secondary windings corresponds to the number of CIM inverters.

EFFECT: improved functionality, increased reliability due to implementation of multichannel circuit with synchronous operation of channels and possibility of load redistribution between channels, due to which increase in efficiency is also provided.

8 cl, 4 dwg

Description

The technical solution relates to the field of converting electronic equipment and can be used to create inverters for alternative sources of electricity.

Solar inverters are well known in the art. Standard elements for such devices are: DC module (input signal), inverter module and AC module (output signal) connected to the transformer.

The DC module includes a number of photovoltaic cells that provide direct current (DC) input to power inverters. The power inverter module uses a series of electronic switches, in particular isolated bipolar transistors (IGBTs), to convert direct current at the input to alternating current (AC) at the output.

For inverters supplying electricity to the electric network, the AC module provides an alternating current output in the form corresponding to the current of the public consumption electric network.

Very often, solar power plants are installed in large areas with difficult climatic conditions, which causes certain difficulties in their maintenance and requires the use of equipment adapted for continuous autonomous operation in difficult operating conditions.

Currently, many approaches are used to increase the efficiency of the photovoltaic elements of solar panels, in particular, control inverter devices based on the determination of the maximum power point (TMM).

String technology is known from the prior art, which is based on a multi-channel system with TMM definition for each channel. The advantages of such a system are increased reliability with an increased efficiency due to the determination of TMM for each array of solar panels, while a large number of individual channels can reduce the dependence of the system on the failure of one or more channels.

Another well-known version of the technology used in modern solar power plants is the use of complete power distribution and conversion devices with a central inverter. This technology allows you to work with large arrays of photovoltaic modules (FEM) but has a significant drawback associated with the use of a small number of channels, which significantly reduces the reliability of the system, since when you turn off one channel, 30-50% of the system power is lost.

The present invention fundamentally combines these two approaches, providing multichannel with a large number of independent channels, each of which works with a separate array of FEM, and is combined into a single system with communication with a public network via a multi-winding transformer with split secondary windings. With all this, the device is mobile and protected from external climatic factors, which greatly simplifies its operation.

Leading manufacturers of solar inverters mainly place their devices in a protected case in the form of a block box, which allows the use of a complete device for the distribution and conversion of electricity in various climatic conditions, providing protection against the effects of harmful environmental factors.

The prior art multilevel step-up three-phase converter of constant voltage to three-phase industrial frequency, RF patent No. 2537506 from 11/19/2012, IPC H02M 7/497. The device described in patent No. 2537506 contains a common DC voltage source in the form of a solar battery connected to a single-phase bridge autonomous inverter, and a three-phase cell-type frequency converter, consisting of a multi-winding transformer, rectifier-inverter cells, a control system, current sensors, voltage and an adjustable regulator quantities. A single-phase bridge autonomous inverter is made high-frequency, a three-phase cell-type frequency converter is connected to its output, a transformer of which is made by a high-frequency single-phase multi-winding and its secondary windings are respectively connected to the inputs of single-phase rectifier-inverter cells consisting of series-connected single-phase rectifier and inverter. The secondary windings of the matching transformer are designed to be connected to the power grid of the power system.

The disadvantages of this technical solution include the use of a single-phase rectifier and inverter with their series connection, which can lead to a significant loss of device power in the event of failure of one of these structural elements.

Also, from the patent for the invention No. 2606383 of 09/01/2015, IPC H02M7 / 493, an inverter for solar power plants is known containing a block of solar batteries connected to an energy converter. The first parallel-connected power module of the energy converter is connected to the first primary winding of the transformer, the second parallel-connected power module of the energy converter is connected to the second primary winding of the transformer, the primary windings of the transformer are connected counter to each other. The secondary winding of the transformer is connected in parallel to a series-connected resistor and supercapacitor.

The disadvantages of the described technical solution include the low reliability of the device, because when one of the power modules fails, the inverter loses 50% of the power.

As the closest analogue, a technical solution was taken, known from the application for invention DE102011083330A1 dated 03/28/2013 IPC H02M7 / 497, according to which, a power distribution and conversion device connected via input switching blocks to arrays of photovoltaic modules (FEM) includes a central inverter module (CIM) with a set of power cells of inverters with sinus filters, the transformer of which the primary winding is connected to the network through the output switching cell, while the secondary windings are connected to CIM uyuschimi inverters, by connecting a star-shifted phases. The pointing device contains 4 inverters connected with a phase shift of 15 °.

The disadvantage of this technical solution can be considered the implementation of a transformer with secondary windings made with a phase shift, which does not allow the synchronous operation of individual channels with a difference of currents on each of them, thus, when a single channel is turned off, the device can lose more than 25% of power.

The technical problem to which the claimed invention is directed is the creation of a complete, multi-functional device for the distribution and conversion of electricity, made with the possibility of several independent channels with increased efficiency, as well as reliable and convenient to use.

The technical result achieved from the implementation of the claimed invention is to expand the functionality, increase reliability by implementing a multi-channel circuit with synchronous operation of the channels and the possibility of redistributing the load between the channels, due to which, an increase in efficiency is also provided.

The essence of the claimed invention lies in the fact that the complete device for the distribution and conversion of electricity connected through input switching blocks with arrays of photovoltaic modules (FEM) includes a central inverter module (CIM) with a set of power cells inverters with sinus filters, the transformer of which the primary winding is included in network through the output switching cell, while the number of secondary windings corresponds to the number of inverters CIM.

According to a preferred embodiment of the invention, each FEM array is connected to at least one CIM inverter, each CIM inverter is connected to a separate secondary winding from among the uncoupled common-mode secondary windings of the transformer, forming independent channels configured to simultaneously operate with currents of different sizes and redistributing currents between the channels, while one of the secondary low-voltage windings is connected with the device for pre-starting the transformer, and is configured to connect peripheral devices.

Also, according to possible embodiments of the invention, one of the secondary low-voltage windings is connected to the transformer pre-start device and provides power to the internal equipment of the entire device.

Independent channels for processing currents of various sizes include elements to reduce the mutual influence of transformer windings.

The input switching blocks contain a dual filter system for high-frequency electromagnetic interference.

The input switching blocks contain a surge protection system based on a varistor circuit.

At the input and output of the inverter cells, switching devices are installed that ensure that individual channels are turned off.

According to a preferred embodiment, the primary high-voltage winding is connected to the network by connecting to a star with the possibility of switching in the triangle when switching to a network with a different rated voltage.

Independent channels for processing currents of different sizes are made with the possibility of working with currents with different phase shifts relative to the main harmonic of the mains voltage.

The essence of the claimed invention is illustrated, but not limited to the following graphic materials:

figure 1 - a complete device for the distribution and conversion of electricity, General view;

figure 2 - schematic diagram of a complete device for the distribution and conversion of electricity;

figure 3 - summing transformer with split windings;

4 is a diagram of a device for pre-charging a transformer.

A complete device for the distribution and conversion of electricity is designed to convert electric energy received from a direct current source into alternating current for transferring it to an energy system with a frequency of 50 Hz, voltage of 10 kV and more.

As a voltage source can be used:

• solar panels based on photovoltaic modules;

• rechargeable batteries;

• supercapacitor batteries;

• DC generators.

The technical solution can be applied at power generating stations. The design of the described embodiment of the technical solution is optimized for labor costs for installation, commissioning and maintenance. The execution of the block box does not require additional construction documentation and expertises for installation at the facility.

The inventive device converts direct current voltage of 680 ... 975 V, in a three-phase voltage of 10 kV or more, industrial frequency.

The technical solution implements the principle of "direct-alternating current" with one output power transformer. Conversion from direct to alternating current is performed by power units (cells) built on IGBT transistors.

According to a preferred embodiment of the invention, the device body is implemented as a block box 1 consisting of a base 2 of a frame structure with wall mounted sandwich panels.

The device case is divided into compartments:

• operator 3;

• introductory switching 4;

• output cell 5;

• power cells of inverters 6 and transformer 7 with a common heating and ventilation system and microprocessor control system;

• ventilation of inverters 8 and transformer 9.

One of the possible variants of the functional diagram of the claimed technical solution is depicted in figure 2. According to the given variant of the scheme, it can be conditionally divided into four blocks.

The first at the input from the side of the FEM 10 arrays is the switching input block 11, which contains a dual system of filters 12 from high-frequency electromagnetic interference (EMC), input current measurement sensors 13, DC isolation isolation control relay 14, and overvoltage protection devices 15 based on varistor circuitry providing protection against lightning strike.

The second from the FEM arrays includes the inverter unit 16, which contains switching devices 17 installed at the input and output of the inverter cells 18, which ensure that individual channels are turned off. This embodiment makes it possible to redistribute the current load between the inverters when they are not fully loaded, bringing it closer to the nominal values, using, thus, part of the inverter modules with optimal load and providing increased efficiency.

The power cells of the inverters are connected to the sinus filters 19. The inverter block 16 is connected to the block of the summing transformer 20 (Fig. 2,3), the primary high-voltage winding 21, which is connected to the network by connecting to a star with the possibility of switching into a triangle when switching to a network with another voltage. The secondary low-voltage winding 22 of the transformer is split and contains n potential in-phase secondary windings, n≥3 corresponding to the number of power inverters of the central inverter module (CIM). Each FEM array 10 is connected to at least one CIM inverter represented by power inverter cells 18 and a sinus filter cell 19, each CIM inverter is connected to a separate secondary winding 22 from the number of decoupled common-mode secondary windings of the transformer, forming independent channels configured to simultaneous operation with currents of different sizes, while the input voltage coming from the FEM arrays is common to all channels. Independent channels for processing currents of various sizes include elements 23 for reducing the mutual influence of transformer windings by increasing the inductance of individual windings. These elements 23 according to one of the possible options for implementation, presented in the form of inductors, magnetically not interconnected. This embodiment allows to ensure stable synchronous operation of all channels, regardless of the current value in each of them.

One of the secondary windings 24 is connected to the transformer pre-start device 25, the circuit of which is shown in Fig. 4 and is configured to connect peripheral devices and provides power to all internal equipment. The specified device 25 at startup provides the same voltage at the output of the transformer as that from the supply network, which contributes to the shock-free inclusion of the transformer in the catering network.

The use of a multi-channel inverter in combination with a multi-winding output transformer under the general control of a central controller allows simultaneous operation of invert channels in different modes, with different tasks for active and reactive current. These capabilities are realized during inspections and tests of the equipment of the block-box directly on the site of installation and operation.

At the output of the device, a block 26 of output switching is included in the functional circuit, which contains a measuring transformer 27 allowing to measure the mains voltage, as well as a high voltage meter 28.

The implementation of the claimed device circuit during operation allows you to implement at least the following features:

- determination of the main voltage harmonic with the implementation of regulation and synchronization with the public consumption voltage network, while the independent channels for processing currents of different sizes are configured to work with currents with different phase shifts relative to the main harmonic of the mains voltage;

- shock-free start-up of the transformer at idle, in which, for a time not exceeding t ≤ 2s, the transformer core is magnetized while limiting the starting currents. After that, the transformer is connected to a 10 kV network using a high-voltage switch;

- accurate synchronization of inverters and the generation system as a whole, on the high-voltage and low-voltage sides of the power transformer;

- switching power devices in neutral modes, whereby they realize, operational shutdown of power switching devices without inrush currents, when switching power cells of inverters. Inclusions of DC contactors are performed when the voltages at the terminals of the FEM array are equal to the voltages at the inputs of the inverter cells without significant inrush currents. The principle of neutral mode allows you to reduce the duration of transients in the power unit during assembly / disassembly of the power circuit or transitions from mode to mode. In general, this extends the life of the equipment of the energy conversion and distribution device.

According to the described implementation option, the claimed technical solution is made with the possibility of working on two TMM inputs, working with two FEM arrays, device variants are also possible with the number of FEM arrays equal to N, where N is the number of CIM channels corresponding to the number of low-voltage secondary windings of the transformer n.

The implementation of the claimed invention contributes to the achievement of the specified technical result, providing increased functionality, providing ample opportunities for energy conversion with the generation, transmission and absorption of active and reactive power. Also, the claimed technical solution allows to increase reliability due to the implementation of a multi-channel circuit with synchronous and independent operation of the channels, while the presence of the possibility of redistributing the current load between the channels provides an increase in the coefficient of efficiency (COP).

Claims (8)

1. A complete device for the distribution and conversion of electricity, connected through input switching blocks with arrays of photovoltaic modules (PEM), including a central inverter module (CIM) with a set of power cells of inverters with sinus filters, a transformer, the primary winding of which is connected to the network through the output switching cell wherein the number of secondary windings corresponds to the number of CIM inverters, characterized in that each FEM array is associated with at least one CIM inverter, each inverter CIM is connected with a separate secondary winding of the number of decoupled in-phase secondary windings of the transformer, forming independent channels, capable of simultaneous operation with currents of varying magnitude, with one of the secondary windings associated with the prior starter transformer and configured to connect peripheral devices. 2. The complete device for the distribution and conversion of electricity according to claim 1 is characterized in that one of the secondary windings is connected to the device for pre-starting the transformer and provides power to the internal equipment of the entire device. 3. The complete electric power distribution and conversion device according to claim 1 is characterized in that the independent channels for processing currents of different sizes include elements for reducing the mutual influence of the transformer windings. 4. The complete device for the distribution and conversion of electricity according to claim 1 is characterized in that the input switching blocks contain a dual filter system from high-frequency electromagnetic interference. 5. The complete electric power distribution and conversion device according to claim 1 is characterized in that the input switching units comprise a surge protection system based on a varistor circuit. 6. The complete device for the distribution and conversion of electricity according to claim 1 is characterized in that switching devices are installed at the input and output of the inverter cells, which ensure that individual channels are turned off. 7. The complete electric power distribution and conversion device according to claim 1 is characterized in that the primary high-voltage winding is connected to the network by connecting to a star with the possibility of switching into a triangle when switching to a network with a different rated voltage. 8. The complete electric power distribution and conversion device according to claim 1 is characterized in that the independent channels for processing currents of different sizes are configured to operate with currents with different phase shifts relative to the main harmonic of the mains voltage.

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