RU2537506C2 - Multilevel step-up converter of dc voltage to three-phase voltage of industrial frequency - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to the converters widely used, for example in solar power. Technical result is achieved due to assurance of work to three phase load and joint operation with three phase grid by means of making the multi-level step-up three-phase converter containing common DC source, for example in form of the solar panel, single-phase bridge self-contained inverter, to its output the additional three-phase converter of cell type is connected, it contains HF step-up single-phase multi-winding transformer, single-phase reversible cells connected with secondary windings of the transformer, control system, current and voltage transmitters, setup unit of output voltage with industrial frequency. The matching transformer of industrial frequency is connected. Number of levels in the output voltage sinusoid is determined by number of single-phase reversible cells in the frequency converter.

EFFECT: improvement of weight and dimension parameters and expansion of functional abilities.

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Description

The invention relates to a conversion technique and can be used to convert the energy of a solar battery into an alternating voltage of industrial frequency in solar energy.

The well-known stand-alone inverter (AI) of the KOMPEL company is used to convert the energy of a solar battery (SB) into a single-phase alternating voltage of industrial frequency (railway Power Electronics, No. 2, 2011, p. 63). A self-contained inverter is a converter containing an input stage with capacitors, an inductance, a transistor switch, a diode and an output stage with a bridge single-phase inverter and an output filter to which a single-phase load is connected. These elements form a single-phase "solar inverter" unit. The disadvantages of the device are the large size of the filters to obtain an output sinusoidal voltage of industrial frequency with low distortion, a stand-alone inverter has large distortion of the output voltage and is not a multi-level.

Known multi-stage (multi-level) single-phase inverter that converts the energy of the SB, consisting of series-parallel connected solar cells (SE) into a single-phase, close to sinusoidal voltage of industrial frequency without the use of dimensional filters [Isembergenov N.T. Multistage inverter for converting solar energy. // Electricity No. 7, 2011].

In this inverter, the formation of the output voltage is carried out by summing the voltages E1 ... En of series-connected sources with solar cells, forming steps, using several transistor single-phase bridge inverters. The summation of the voltages is carried out on the total load Rn, taking into account the different switching times of the steps of individual inverters in accordance with the control algorithm. As a result, such a multi-stage inverter unit generates a single-phase voltage close to a sinusoidal shape. Here, ASE-50 series solar cells with a voltage of 17 V and a current of 2.88 A are used. For example, to obtain an output power of 6 kW with a voltage of 220 V, 180 SE must be connected to a battery.

Similarly, a further increase in power and voltage at a single-phase load is performed.

For the formation of a three-phase step-up multilevel inverter, it is possible to use, for example, three single-phase units connected to a common DC voltage source, and connect their outputs to the windings of an additional three-phase step-up transformer (or three single-phase) of industrial frequency, transmitting the source power and the required voltage level to the load [ G.S. Zinoviev. Fundamentals of Power Electronics, Novosibirsk, 2003, sheets 435-437].

The disadvantage of this device is that the inverter does not provide power to the three-phase load, and the additional introduction of a three-phase industrial frequency transformer worsens the overall dimensions. In addition, the symmetry and sinusoidality of the output voltage curve depends on the identity of the magnitude of the voltages E1 ... En. In practice, this is difficult to achieve, especially at high capacities with a large number of solar cells located in large areas with varying degrees of exposure. In the case of a common power source, a change in the voltages of individual SCs causes a change in the total total voltage E, but does not affect the shape of the individual stages of the inverter voltages, as a result, the sinusoidal shape of the output voltage is not violated. Moreover, the stabilization of the value of the output alternating voltage is carried out due to the regulation system.

The closest in technical essence and taken as a prototype is a multilevel three-phase frequency converter of a cell type, used in a frequency-controlled (VFD) type ABS - DRIVE to control the speed of an electric motor [Kalsin V.N., Matison A.G., Shepelin V.F. . and other Works of VNIIR OJSC of ABS Electro in the field of high-voltage electric drive and power electronics, Journal of Electrotechnics, 2011, No. 1]. In the prototype, the VFD receives power from a 50 Hz network through a multi-winding three-phase transformer. The frequency converter is based on rectifier-inverter cells having a three-phase rectifier at the input of the cell. The formation of a multi-level output voltage in each phase is carried out by summing the voltages of the individual stages using a control system, current sensors, voltage and a master device.

The disadvantages of the prototype are the large weight and size indicators of the transformer at a frequency of 50 Hz and limited functionality due to the lack of the ability to power from a common DC voltage source or DC network.

The technical result of the proposed solution is the improvement of overall dimensions and the expansion of functionality by providing power from a common source of constant voltage and / or DC network, working together with a three-phase network of the power system.

The technical result is achieved by the fact that in a multilevel step-up converter of direct voltage into a three-phase industrial frequency, containing a common source of direct voltage, for example, in the form of a solar battery connected to a single-phase bridge autonomous inverter made by high-frequency, the output of which is connected to an additionally introduced three-phase cell frequency converter type consisting of high-frequency boost single-phase multi-winding transformer, single-phase rectifier o-inverter cells connected to the secondary windings of the transformer, wherein each cell includes a serially coupled between a single-phase rectifier and an inverter and an additional power frequency matching transformer, secondary windings of which are intended for connection to the electrical power system.

A distinctive feature of the present invention is that the introduction of a high-frequency, for example 1000 Hz, single-phase autonomous inverter and transformer, as well as the introduction of a high-frequency converter into a three-phase voltage of industrial frequency with single-phase rectifier-inverter cells and ensuring collaboration with the corresponding three-phase industrial network as directly and / or with an additional matching transformer provides the improvement of overall dimensions and expansion rhenium functionality. When supplying a load, for example, voltage of 380 V, 50 Hz and the need to work together with the power grid of the power system, for example, with voltage of 110 kV, 50 Hz, it is advisable to use a matching transformer. The essence of the proposed solution is illustrated in figure 1, 2, 3, where the following notation:

1 - a constant voltage source, for example, SB,

2 - autonomous bridge single-phase inverter, with a frequency, for example, f1 = 1000 Hz,

3 - high-frequency transformer with a frequency f1,

4 - secondary windings of the transformer 3,

5 - block rectifier-inverter cells,

6 - rectifier-invertor cell,

7 - control system,

8 - voltage sensor,

9 - current sensor,

10 - power frequency voltage adjuster (or control panel),

U, I, Uy - output signals of elements 8-10,

U1 - output voltage of a multilevel converter,

ABC - output terminals of the device,

Figure 2 presents a diagram of a cell 6, where

11 - three-phase converter of industrial frequency,

12 - bridge single-phase rectifier,

13 is a capacitor

14 - bridge single-phase transistor inverter,

15 - load

16 - matching three-phase transformer,

17 - primary winding,

18 - secondary winding

19 - power system

Uo is the output voltage of the inverter 14.

Figure 3 presents a functional diagram for working on a load (for example, load 15 (an electric motor with a voltage of U1 = 380 V, 50 Hz) and on the power system 19 (for example, with a voltage of U2 = 110 kV, 50 Hz) through a matching three-phase transformer 16 with a primary winding 17 and a secondary winding 18.

The multilevel step-up three-phase converter of direct voltage into three-phase industrial frequency contains a common source of constant voltage, for example, in the form of a solar battery 1 connected to an autonomous bridge single-phase inverter, with a frequency, for example, f1 = 10002; high-frequency transformer with a frequency f1 3 with secondary windings 4; block of rectifier-inverter cells 5 with rectifier-inverter cells 6, control system 7, voltage sensors 8 and current 9, voltage regulator of industrial frequency 10, while a stand-alone bridge single-phase inverter 2 and transformer high-frequency transformer with a frequency of f1 3, the secondary windings of the transformer 4 are respectively connected to the block 5 of the rectifier-inverter single-phase cells 6, the outputs of which are interconnected in series in three groups and form a three-phase industrial frequency converter 11 with the output E ABC phase terminals connected to the load 15 and may connect a corresponding network of industrial frequency for the collaboration. Cell 6 is a series-connected single-phase rectifier 12 and a bridge single-phase transistor inverter 14, when an additional matching three-phase transformer 16 is turned on, its primary windings 17 and load 15 are connected to the output terminals of the ABC of the frequency converter 11, and the secondary windings 18 are connected to the power system.

The proposed device operates as follows. The energy source in the device (Fig. 1) is a common DC link, in this case, a solar battery (SB) 1, which is formed from individual solar cells. An autonomous bridge single-phase inverter 2 converts a constant voltage of the SB into an alternating high-frequency voltage, for example, 1000 Hz.

At the output of an autonomous bridge single-phase inverter, with a frequency, for example, f1 = 1000 Hz 2, a single-phase high-frequency transformer 3 is connected, which provides power to each cell 6 (Figs. 1, 2) from the individual secondary windings 3 of the transformer 4.

The outputs of the cells 6 are connected in series into three groups and a star, forming together with the control system 7, sensors 8, 9 and the setter 10 a frequency converter 11 with output terminals ABC, on which we obtain an industrial frequency voltage, for example, 50 Hz. The control system 7 provides PWM regulation of the transistor inverter 14 (figure 2). At the outputs of cells 6, various combinations of three signals are formed (+ Uo, -Uo and 0). These signals are summed up and create a multilevel system of output three-phase voltage of industrial frequency.

The number of output voltage levels is determined by the number of cells: at 15 cells in block 5, the output sinusoidal linear voltage has 11 steps (levels) - a common zero step and 10 steps in each positive and negative half wave of the sine wave. The voltage amplitude of a multilevel sine wave is 10 Uo.

The load 15 is connected to the terminals of the ABC (Fig. 3) and, if necessary, joint work with the network - the corresponding network, for example, 380 V, 50 Hz. In some cases, it is necessary to connect this high power device to the power system 19 with a high voltage, for example, 110 kV, 50 Hz, which provides a matching transformer 16.

Claims (2)

1. A multi-level step-up three-phase converter of direct voltage into a three-phase industrial frequency, containing a common source of constant voltage, for example, 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, control systems, current, voltage, and variable speed drives, characterized in that the single-phase bridge autonomous inverter is full of high-frequency, a three-phase cell-type frequency converter is connected to its output, the transformer of which is made of 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. 2. The device according to claim 1, characterized in that it further comprises an industrial frequency matching transformer, the secondary windings of which are designed to be connected to the power grid of the power system.

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