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Power Electronic Drives (EET421) Laboratory Module EXPERIMENT 3 Single-Phase Semiconverter with DC Motor Load Objective : To evaluate of a DC motor controlled by adjusting the DC voltage supply, using a bridge rectifier for full-wave rectification and an SCR. To analyze its harmonics and power factor characteristics. Introduction : A DC motor normally contributes to spikes, voltage disturbances, harmonics , low PF to the main power system and lower the power supply quality. In this particular experiment, an AC supply source with different voltage selection is used to supply DC voltage to a DC motor through a single-phase semiconverter (as an AC to DC power converter). The motor with a rectifier bridge should have different performance and characteristics. The speed, harmonics, total harmonic distortion (THD) and power factor should be observed as these will have significant impact of affecting the motor and power system. A single-phase full wave rectifier plus a SCR that supplies a very high inductive load such as a dc motor load is shown in Figure 1.1. This circuit is known as a single phase semiconverter, and it is commonly used in industrial applications especially for speed regulation. D1 A C iD1 is D3 Field winding Vs D4 L M D2 Figure 1.1 Single-phase semiiconverter with DC motor load With resistive load, the load current is identical in shape to the output voltage. In practice, most loads are inductive load to a certain extent and the load current depends on the values of load resistance RL and load inductance L. UNIVERSITI MALAYSIA PERLIS – Exp.3 1 Power Electronic Drives (EET421) Laboratory Module The average output voltage can be found from Vdc Vm (1 cos ) (1-1) where Vm is maximum supply voltage and α is firing angle. The average output current I dc Vdc RL (1-2) The output dc power, Pdc = Vdc Idc (1-3) The rms output voltage is found from Vrms V 1 sin 2 m 2 2 1/ 2 (1-4) The ripple factor is defined then as Vrms Vdc 2Vm 2 RF 2 (1-5) The instantaneous input current can be expressed in a Fourier series as is (t ) ao (a n 1, 2,.. n cos nt bn sin nt ) (1-6) The first part of equation (1-6) is the average input current and the second part is the ripple content on the input current. The total harmonic distortion in line current is then I rms ,tot THD I rms , fund 2 1 UNIVERSITI MALAYSIA PERLIS – Exp.3 2 Power Electronic Drives (EET421) Laboratory Module Equipment and Parts : 1) Single-phase 5 kVA programmable power source. 2) SCR Speed Controller ED-5113 3) DC Motor DCM-250 4) Variable Resistance Load ED-5101 5) DC Volt/Ampere Meter ED-5105 6) Tacho-Meter ED-5118 7) Wires Procedure : Warning : High voltage are used in this laboratory experiment Do not make any connection with the Power ON Please ask the Teaching Engineer or the Technician to check your circuits before turning on the supply for all the tests 1) Connect the circuit as given below in Fig 1.0. 2) In the first part of this experiment, connect the primary side of the transformer to the output of the 5 kVA programmable power source and the output of the converter to 600 Ohm resistive load. 3) After ensure your connection is correct, turn-on the power of the AC supply to 5 kVA programmable power source equipment (single phase and three-phase) and the ac power supply for personal computer. 4) Please inform the teaching engineer or the technician when need to check the connections. Transformer A ~ AC V 150V 230V M = Rectifier Saffner Harmonic Analyzer Fig 1.0 : Circuit connection UNIVERSITI MALAYSIA PERLIS – Exp.3 3 Power Electronic Drives (EET421) Laboratory Module 5) Before Pressing OK button on the Test Screen to start a test of step 5 of manual, the voltage setting must be suited as that has been decided. (look on the table 1.0) 6) Adjust the potensiometer (circuit control) on 6 position 7) Referring to the Table 1.0, record the readings accordingly. You will need the AC supply voltage (Vrms) of 40Vac, 50Vac, 60Vac, 70 Vac, 80 Vac, 90 Vac, and 100Vac for the data. These voltages are set from single-phase 5 kVA programmable power source. Table 1.0 For 300 Ohm Resistive load Vout Vrms 40 50 60 70 80 90 100 Iout THDv THDi W PF 8) In the second part of the experiment, replace the resistive load with DC motor. 9). The firing (delay) angle of the SCR is fixed for all of AC supply voltage. 10) Referring to the Table 1.1, record the readings accordingly. You will need the AC supply voltage (Vrms) of 40Vac, 60Vac, 80Vac, 100 Vac, and 110Vac for the data. These voltages are set from single-phase 5 kVA programmable power source. Table 1.1 For DC motor load Vrms 40 60 80 100 110 Vout Iout Speed THDv THDi W PF 11) Using the equation (1-1), prove that the multimeter DC voltage value is similar to the equation. 12) Is it similar or not ? Make a statement to either of your answer. UNIVERSITI MALAYSIA PERLIS – Exp.3 4 Power Electronic Drives (EET421) Laboratory Module 13) After you have completed the table, plot graphs of speed against voltage, speed against current and current THD (THDi) against speed and voltage against power. 14) Explain the behaviours of each graph that you have plotted. 15) Please state your conclusion for the whole of this experiment, including your comparisons and differences (with reasons) of THDv, THDi and PF between resistor and DC motor loads. UNIVERSITI MALAYSIA PERLIS – Exp.3 5