RU2771617C1 - Single-phase inverter with pulse-amplitude modulation - Google Patents

Abstract

FIELD: power electronics.

SUBSTANCE: invention relates to the field of power electronics and is designed to generate voltage with a low content of harmonic components. A single-phase inverter with pulse-amplitude modulation containing a switch consisting of three series-connected cells, each of which includes a series-connected capacitor and a transistor with a reverse shunt diode, three transistors with reverse shunt diodes connected to the corresponding switch cell in phase with respect to the cell transistor, while the switch is connected to the power buses of a single-phase bridge inverter with an output load, and a single DC voltage source is connected through the reactor, a diode and a transistor with a reverse diode of the last cell of the switch to the power buses of the inverter bridge.

EFFECT: reducing the hardware costs and the cost of the inverter.

1 cl, 3 dwg, 1 tbl

Description

The invention relates to the field of power electronics and is intended to generate voltage with a low content of harmonic components.

Known multi-level voltage inverter with floating capacitors [1], including a chain of series-connected power switches with reverse shunt diodes and a set of independent capacitors, pairwise shunting power switches, which ensures low switching losses. The disadvantages of this inverter are high weight and size and the cost of the inverter due to the presence of a large number of capacitors in the circuit.

A multilevel voltage inverter with clamping diodes is also known [2]. This inverter has lower weight, size and cost compared to the inverter with floating capacitors, but has large switching losses.

Also known is a multilevel cascade bridge voltage inverter, consisting of series-connected single-phase bridges [3]. Each bridge has a separate DC voltage source and consists of four power controlled switches with reverse shunt diodes. The disadvantages of such an inverter are high hardware costs and significant switching losses due to the presence of a large number of power switches.

Also known eight-level single-phase voltage inverter [4]. The disadvantages of such an inverter are increased hardware costs due to the need to have three galvanically isolated DC voltage sources.

Closest to the proposed invention is an inverter consisting of a switch and a bridge, the diagram of which is shown in Fig. 8.146 in [5]. The switch includes n cells, each of which contains a constant voltage source with a capacitor at the output and a transistor shunted by a reverse diode and connected in a conductive direction with respect to the power source. In addition, the switch contains n AC switches, each of which shunts its cell and allows you to work on an active-inductive load. This inverter can provide more output voltage levels than the circuits discussed above with an equal number of DC voltage sources.

However, the presented inverter circuit is characterized by excessive hardware costs caused by the need to have n constant voltage sources to obtain a multi-stage output voltage curve, as well as the use of alternating current switches in the circuit. Hardware costs increase especially significantly if rectifiers are used as sources of constant voltage, which, moreover, must be galvanically isolated. In addition, the work does not show the timing diagrams of the operation of the keys, and there is no information about the quality of the generated voltage.

The object of the present invention is to reduce the hardware and cost of a voltage inverter with a near-sinusoidal stepped output voltage curve.

The problem is solved by replacing n AC voltage sources with one source with a diode and a reactor connected in series with it in the conductive direction, and the negative output of the power source is connected to the negative bus of the inverter bridge, and the positive output through the reactor, diode and transistor is connected to the positive bus of the inverter. In addition, the achievement of this goal is ensured by replacing the alternating current switches with transistors shunted with reverse diodes and each connected in parallel and out of phase with one of the switch cells.

The essence of the invention is illustrated by drawings: Fig. 1 is a diagram of an inverter generating a step-shaped voltage having 8 levels per half-cycle, counting the zero level, FIG. 2 is a plot of the output voltage of the inverter, in FIG. 3 - timing diagrams of inverter key control.

The voltage inverter contains:

- switch 1, consisting of three series-connected cells, each of which includes a series-connected capacitor (4, 5 or 6) and, accordingly, a transistor (7, 8 or 9) with a reverse shunt diode (13, 14 or 15), and also transistors 10, 11, 12 with reverse shunt diodes 16, 17, 18 connected in parallel with the corresponding cell in the opposite direction with respect to transistors 7, 8 and 9, respectively;

- single-phase bridge inverter 2 with load 3 at the output, consisting of transistors 19-22, shunted by reverse diodes 23-26, the power buses of which are connected to the outputs of the switch;

- the only constant voltage source 27 connected through the reactor 28, the diode 29 and the transistor 9 with a reverse diode 15 of the last switch cell to the power buses of the inverter bridge 2.

In the key management timing diagrams of FIG. 3, the letters a, b, c, d, e and f respectively indicate the control signals of transistors 7, 10, 8, 11, 9 and 12 of the switch 1, and the letters g and h indicate the control signals of pairs of thyristors 19, 22 and 20, 21 of the bridge 2 respectively. The switching angles of transistors 7-12 are selected based on the criterion of minimizing the coefficient of harmonic components of the output voltage of the inverter. From the diagrams of Fig. 3 shows that transistors 7 and 10, 8 and 11, 9 and 12 operate out of phase, and their switching frequencies differ.

Inverter capacitors 4, 5 and 6 are charged from source 27 through reactor 28 and diode 29. The capacitances of the capacitors are selected from the condition of obtaining the levels of steps necessary to minimize the harmonic coefficient of the output voltage of the inverter bridge.

Let us consider the device operation process using the example of the second quarter of the inverter operation period, when the voltage applied to the load decreases, which leads to the need to return the reactive energy accumulated in the inductive part of the load to capacitors 4, 5 and 6. In the first quarter of the period, switching occurs in the reverse order (Fig. 2).

In the range of 71-109 degrees, transistors 7, 8, 9 are open. As a result, the total voltage of capacitors 4, 5 and 6 is applied to the inputs of the inverter bridge 2, forming the largest eighth stage of the output voltage.

In the range of 109-123 degrees, transistors 8 and 9 are open, and transistor 7 is closed. As a result, the total voltage of capacitors 5 and 6 is applied to the inputs of the inverter bridge 2, forming the seventh stage of the output voltage. The reactive power accumulated in the inductive part of the load in the previous interval is returned to capacitors 5 and 6 through diodes 15 and 14 and an open transistor 10.

In the range of 123-136 degrees, transistors 7 and 9 are open, providing the application of the total voltage of capacitors 4 and 6 to the inverter bridge, which forms the sixth stage of the output voltage. Reactive load currents are returned to capacitors 4 and 6 through the switched on transistor 11 and diodes 13 and 15.

In the range of 136-148 degrees, transistor 9 is turned on, and transistors 7 and 8 are turned off. Thus, the voltage of capacitor 6 is applied to the input of the inverter bridge 2, forming the fifth stage of the output voltage. The return of reactive load power to capacitor 6 is provided by open transistors 10 and 11 and diode 15.

In the range of 148-159 degrees, the voltages of capacitors 4 and 5 are connected to the input of the inverter bridge 2 through open transistors 7 and 8 and diode 18. Thus, the fourth stage of the output voltage is formed. To return the reactive power of the load, transistor 12 remains open in this interval.

In the range of 159-169 degrees, transistor 7 is turned off, and transistor 8 is turned on. As a result, the voltage of capacitor 5 is applied to the input of the inverter bridge through transistor 8, diodes 16 and 18, which exceeds the voltage on capacitor 4 twice, which ensures the formation of the third stage output voltage. Transistors 10 and 12 are open in the same interval, providing a return of reactive energy accumulated in the load to capacitor 5.

In the range of 169-178 degrees, transistor 7 is open, and transistor 10 is off. As a result, the voltage of the capacitor 4 through the transistor 7 and the diodes 17 and 18 is applied to the bridge 2, forming the second stage of the inverter output voltage. Transistors 11 and 12 are also open in this interval, providing channels for returning reactive load currents to capacitor 4 through diode 13.

In the range of 178-182 degrees, transistors 7, 8, 9 are off, and 10, 11, 12 are on. As a result, zero voltage is applied to bridge 2, and the energy accumulated in the inductive part of the load is circulated through the corresponding diodes 23 and 26 of the bridge and transistors 12, 11 and 10. Thus, in the range of 0-2 degrees, the load is short-circuited by these diodes.

In the second half-cycle, the switching of transistors 7-12 occurs in the same order as in the first half-cycle. However, transistors 19, 22 of bridge 2 are turned off, and transistors 20 and 21 are turned on, so that a negative voltage is generated on the load.

The proposed inverter circuit generates a step voltage that has 8 levels per half period, including a zero level step, which provides a total harmonic coefficient of 6.67%, taking into account the entire range of spectrum components. The values of the harmonic components of the output voltage spectrum are given in Table 1.

Thus, the generated voltage satisfies the requirements of GOST R 54149-2010 on the harmonic composition of the voltage for low and medium voltage electrical networks, with the exception of harmonic 15, which is quite easy to filter, given its high frequency.

Information sources

1. Meynard T., Lavieville J.-P., Carrere P., Gonzalez J., Bethoux O. Electronic circuit for converting electrical energy. U.S. Patent 5 706 188, January 1998.

2 Baker R.H. High-Voltage Converter Circuit. U.S. Patent 4 203 151, May 1980.

3. Baker R.H. Electric Power Converter. U.S. Patent 3 867 643, February 1975.

4. Golembiovsky Yu.M., Shcherbakov A.A. Single-phase inverter with stepped output voltage; Utility model patent RU 130159 U1 dated 01/09/2013.

5. Moin B.C. Stabilized transistor converters / B.C. Moin. - M.: Energoatomizdat, 1986. - 376 p.

Claims (1)

A single-phase inverter with pulse-amplitude modulation, containing an inverter bridge and a switch connected to its power inputs, characterized in that the switch contains three series-connected cells, each of which consists of a series-connected capacitor and a transistor shunted by a reverse diode; at the same time, a transistor with a reverse diode is connected to each cell of the switch in antiphase with respect to the transistor of the switch cell; a single source of constant voltage is introduced, connected through a reactor, a diode and a transistor with a reverse diode of the last switch cell to the power buses of the inverter bridge.

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