Design of pulse width converter

Contents

Introduction

1 Analysis of technical solutions for the power part of the converter, calculation of elements

1.1 Short classification of transducers by the specified type

1.2 Analysis of technical solutions options

1.3 Development of schematic diagram of electrical power part of the converter

1.4 Development of electrical functional control system diagram

1.5 Calculation and selection of elements of the power part of the converter

1.5.1 Calculation of parameters and selection of transformer

1.5.2 Calculation and selection of thyristors and diodes

1.5.3 Selection of smoothing and switching capacitor and throttle

1.5.4 Calculation and selection of protection elements

2 Mathematical modeling of the power part of the converter

2.1 Development of equivalent circuit for replacement of power part of converter

2.2 Development of mathematical description of the power part of the converter

2.3 Development of mathematical model and calculation of electromagnetic processes

3 Calculation of adjustment and external characteristics of the converter

3.1 Calculation of adjustment characteristics

3.2 Calculation of external characteristics

4 Calculation of energy characteristics of the converter

4.1. Calculation of efficiency dependence on control action

4.2. Calculation of functional dependence of power factor on control action

Conclusion

List of used literature

Appendix A

Mathematical model

Introduction

Currently, DC electric drives are gradually displaced by AC electric drives, but DC motors still remain the main converters of electric energy into mechanical energy in small and medium-power electric drives.

To power such electric drives, AC-to-DC conversion and other forms of conversion are used using various types of valve plants, and therefore, saving electricity in converter plants and their power supply systems, increasing their efficiency and power factor are the most important tasks. The increase in efficiency is currently achieved by the introduction into production and operation of highly economical semiconductor valves.

In addition to valves, converters usually contain transformers, throttles, capacitors and other electrical elements. However, the valves are the main elements controlling the energy flows and generating the output voltages and currents.

Action of valve converters consists in alternating conductivity of valves of different phases, which thus form curve of output voltage from sections of voltage curves of these phases.

Alternating conductivity of the valves leads to periodically repeated electromagnetic transients. Therefore, the steady state mode of the valve converter is understood to be such a mode of operation when transients due to

by switching the gates, are identical. This mode of the converter is sometimes called quasi-stable.

Upon assignment of the course design, it is necessary to design a non-revertive pulse width converter.

Terms of Reference:

Parameters of PBST-23 engine

Rated rotation speed n = 1500 rpm

Rated voltage Uy = 110 V

Rated power of Rn of =0.85 KW

Rated current of Iya =9.2 A

Resistance of armature windings at 15 ° С Ry = 0.594 Ohm

Resistance of additional poles at 15 ° С Rdp = 0.367 Ohm

Excitation winding resistance at 15 ° С Rov = 216 Ohm.

In addition, it is necessary to investigate the dependence of the efficiency of the PWT on the power loss for switching.

Analysis of variants of technical solutions for the power part of the converter, calculation of elements

1.1. Short classification of transducers by specified type

Pulse width converters are designed to change the value of the DC voltage. They serve to supply the load with a constant voltage different in magnitude from the source voltage.

Depending on the type of semiconductor devices used in the power part, pulse converters are divided into transistor and thyristor. According to the task, it is necessary to design a thyristor PIS.

Thyristor spares are divided into non-reversible and reverse. According to the task, it is necessary to design a non-revertive PIS.

Conclusion

The designed converter is characterized by the following:

Maximum converter efficiency corresponds to maximum duty cycle value;

protection against short-circuit currents and overload currents;

control circuit is protected from short-circuit currents;

an uncontrolled rectifier is used to power the motor excitation winding;

thyristors are protected from short circuit by fast-acting fuses, and RC chains are used to protect against overvoltage that can occur on semiconductor valves.

Non-reversible SPICs convert a smoothly changing input voltage into a pulse voltage with constant amplitude and polarity, but with different duration and they can be divided into two groups - parallel and serial.

In consecutive spares, the operating valve is switched on in series with the load. A characteristic feature of such spares is the inability to obtain an output voltage above the power supply voltage.

In parallel spares, the operating valve or accumulating throttle is switched on in parallel with the load. In such spares, it is possible to obtain a voltage at the output above the voltage of the power source.

Depending on the implementation of switching nodes, thyristor SPICs can be divided into converters with dependent switching nodes (dependent) and converters with independent switching nodes (independent).

In the first, the switching capacitor, while maintaining a negative voltage on the locked thyristor, is recharged by the load current, and in the second, by the current of the oscillating circuit.

In dependent spares, the duration of the capacitor recharge process is inversely proportional to the load current and at low load currents, their operation is difficult.

Independent spares allow operation in idle mode, since the switching capacitor in them is recharged by the current of the oscillating circuit, and not by the load current.