NTC-07.25 “Basic electric drive and converting equipment with MPCS”

1. Frequency converter, which is used to form three-phase AC power line of regulated frequency and power voltage of asynchronous electric motor. The converter is based on the microcontroller MB90F562 (Fujitsu), power intelligent module PS11033 (Mitsubishi). 
The controller is used to count input (voltage, frequency and dynamic braking current setting), output (current, voltage) converter signals, organize data exchange with PC, display the measured values on the front panel of the training system.

The power module consists of power circuits of three-phase bridge inverter, based on IGBT-transistors, drivers circuits and protection from short-circuit current, insufficient voltage of drivers supply, fault injection of the control signals.

Frequency converter provides the investigation of asynchronous electric motor in all four quadrants of mechanic characteristic, and realizes the dynamic motor braking with regulated current.

2. Two pulse-width converters are used to supply armature circuits, excitation winding of DC electric motor or active-inductive load. Pulse-width converters are based on the frequency converter. Two its arms are used for reversible PWC, another arm is used as non-reversible PWC to supply DC motor excitation winding.

Reversible PWC may operate in symmetrical (alternate diagonal inclusion) or non-symmetrical (diagonal inclusion of one resistors pair) modes.

3. Three-phase  controlled rectifier is used to investigate the operation in active, inductive and motor load. The rectifier is based on the microcontroller ATMega163 (Atmel) and load thyristors Т122-25. The controlled rectifier has two operating modes: three-phase MCU-controlled, one-phase with analogue system of phase-pulse regulation. 

4.  Measurement module, based on the digital measurement equipment, is used for current measurement and display in excitation winding of DC motor, for current and voltage measurement between pulse-width converters and frequency converter.

5. Relay-contactor control allows to operate: 

• DC electric motor resistor start in three levels in the function of current, electromotive force, time;
• dynamic braking of DC electric motor in the function of current, electromotive force, speed, time;
• DC electric motor braking by back connection;
• dynamic braking of asynchronous electric motor, plugging braking. 

  Microprocessor unit control of relay-contact control allows to: 

• measure current, voltage, DCM speed and save them with the range of 0,1 sec during 10 seconds (total is 100 values) after the start/braking. It allows to construct the graphics of the start/braking without PC;
• produce analogue signals proportional to current and DCM speed; investigate servo driver system, based on the DCM. Speed measurement is carried out on the signals of the pulse position sensor (360 pulses per revolution).

6. Analogue regulators are used to investigate: 

• closed single-circuit system of current stabilization of DC electric motors;
• closed single-circuit system of speed stabilization of DC electric motor with speed regulator;
• closed double circuit system of speed stabilization of DC electric motor with speed and current regulator. 

Analogue regulators have regulated proportional, proportional-integral inverse current and speed connections.

7. Resistors in armature circuit (three levels).
8. Resistor of dynamic braking of DC electric motor.
9. Power starter of relay subsystem.
10. Power discharge resistors in overvoltage on intelligent module.

Electric schematics of investigated objects are shown on the front panel of the training system. All the schematics are divided into the groups according to the theme of conducted laboratory experiments. Switch sockets, digital equipment indicators, switch gear apparatus, controls, allowing to change elements parameters during laboratory experiment, are installed on the panel. The test points of input, intermediate, output signals of power converter equipment are located on the front panel.

The test points:

• input signal of reversible pulse-width converter;
• control signals from the microcontroller to the drivers of intellectual module of all keys of reversible pulse-width converter;
• voltage and current at the output of reversible pulse-width converter;
• voltage and current at the output of frequency converter;
• control signals from the microcontroller to the drivers of intellectual module of frequency converter;
• the signals of phase-pulse regulation of thyristor rectifier;
•  control signals from the microcontroller to the thyristors;
• current and voltage at the output of thyristor rectifier;
• the signals in closed system of subordinate regulation.

The controls on the front panel:

• setting potentiometer to control the reversible pulse-width converter, tumbler of the converter operating mode (independent/symmetrical);
• setting potentiometer of pulse-width converter to supply the excitation winding of DC electric motor (0 ÷ 500 mА);
• setting potentiometers of the frequency converter, allowing smoothly change the output frequency setting (0 ÷ 89 Hz), output voltage (0 ÷ 220 V), current of dynamic braking of asynchronous electric motor with squirrel-cage rotor (0 ÷ 5 А);
• setting potentiometers of setting signal of closed system, coefficient regulation of inverse current and speed connection;
• setting potentiometer of opening angle of thyristor regulator, tumbler of the operating mode of the regulator (digital three-phase/ single-phase analogue);
• the controls of stopwatch and three starting levels;
• relay subsystem controls.

To conduct the laboratory experiment it’s necessary to assemble the schematic of investigated object, using jumpers, which allow to introduce the schematic in visual form.

Laboratory experiment may be conducted in manual mode and in the mode of the dialogue with PC.

The laboratory training system is supplied with a set of methodical and technical documentation for teaching staff.
 
The software provides the possibility to:

• repeat basic theoretical principles studied in lab;
• check students’ knowledge before conducting laboratory experiments (theoretical questions, correct circuit assembly, knowledge of hardware, step by step control of understanding the selection of the experiment circuit and measuring instruments for the implementation of specific learning objectives);
• conduct laboratory experiments of various difficulty levels:
• implement real-time mathematical calculations of measured electrical quantities and their graphic display;
• save the data obtained and work with them when the bench is off;
• export the data obtained (graphs, oscillograms, estimates) to Office programs in order to provide convenience of subsequent reporting.