Description:
Brief Description: In our case we have developed Experimental /Laboratory setup for single phase thyristor controlled DC Drive .The whole drive can be subdivided into several sections as mentioned below:-

1) Power Supply section.
2) Ramp Generator section.
3) Speed Controller section
4) Current Controller section
5) Firing Pulse generation section.
6) Regulator Inhibit section
7) Pulse Inhibit section
8) Thyristor Bridge section, and
9) dv/dt section i.e. Snubber circuit.

Power Supply Section:-
In this section step down AC voltages are fed to this circuit and +-15 Volts and +-24 voltages are generated. These regulated voltages are fed to different PCBs.
The rectifier circuit for Field voltage is included within the PCB. The PCB is also equipped with Field Loss Relay. The purpose of Field Loss Relay is to protect the motor .The contact of the relay is so interlinked, that, when there is no field current, the main contractor for armature circuit cannot be energized. The layout of this PCB (PCB No.: LDRAB 003) and circuit of it (Circuit No.: CDRAB 003) is given at Fig. no. 3 & Fig. No.:4 respectively).
Ramp Generator:-
The purpose of the RAMP generator is to apply speed reference signal gradually at the input of speed amplifier. The speed reference signal can be directly applied to the speed amplifier input but the main problem is, that, if accidentally large ref. voltage is applied at the input, the motor, attached with the machine, will attain high speed all of a sudden causing speed synchronizing problem with other section which is placed in tandem with the main machine and machine may stop immediately. In practical case the speed reference potentiometer is slowly increased by the operator according to past experience about the behavior of the machine, but it is incorporated here to tackle the situation like careless operation or accidentally setting the potentiometer at high end, by mistake.

Speed Controller Section:-
Ramp generator output is applied at inverting input of 2nd OPAMP.
Actual feedback signal is fed back to the same inverting input but of opposite polarity. For actual feedback signal there are three different input terminals. According to the max. available feedback voltage, a particular terminal is to be selected for connection.
The OPAMP is used as ERROR amplifier with PI Controller. PI section is to be adjusted at the time of commissioning with the actual motor to get smooth response. This is the most critical adjustment. Fine adjustment of maximum speed is carried out by means of Rp5.

Current Controller Section:-
Speed Amplifier output is applied at inverting input of the 3rd OPAMP.
Actual current feedback signal from the current transformer is rectified and fed back to the same inverting input but of opposite polarity. The error signal is produced according to the two inputs. The output is generated according to the PI action of current amplifier. The PI circuitry of the current control has a time coefficient of 22ms, sufficient for the most common applications. The current can be limited by potentiometer Rp3.
The RAMP, Speed controller, Current controller & Regulator Inhibit sections are included in Circuit No: CDRAB 001 and shown in Fig.5. The layout of the PCB(LDRAB 001) is given at Fig.6.
Firing Section:-
In this section the gate pulses are generated for the thyristors. The error signal from Current amplifier is fed to this section. We have used UAA145 IC for generating PWM output. The synchronizing voltage from step down transformer is fed to pin no 9 of the IC. The synchronizing voltage is required for getting the zero cross over points of the incoming AC signal. The Saw tooth voltage is produced inside the IC in synchronism with the zero cross over point. The output of Current amplifier is variable DC voltage. But for firing of thyristor, the delayed firing pulses have to be generated w.r.t. zero cross over point i.e. variation along time axis is required. To convert the variable amplitude signal to corresponding Pulse Width Modulated or Pulse Position Modulated signal, the error signal is compared with the Saw tooth. All the above operations are carried out inside UAA145 IC chip. Two PWM output signals for two half of the ac waveform are available at Pin no. 10 and Pin no. 14 of the said IC.The PWM generated from the IC is low frequency signal which is substantially attenuated when passed through the Pulse transformer. Pulse transformer is used for isolation between Power section at Thyristor- bridge and Electronic Control Section. CD4011 NAND gate IC is used to chop the PWM output at high frequencies which can be easily passed through the Pulse transformer. The secondary of pulse transformer is fed to the gate of the thyristor for firing the same.The Firing Section and Pulse Inhibit section are included in Circuit diagram (CDRAB 002) and Layout diagram (LDRAB 002) and are placed at Fig. No. 7 & 8 respectively.
Bridge Section:-
There are two types of Bridges-i)Full Controlled type and ii) Half controlled or Semi-Controlled type.
A fully-controlled converter or full converter uses thyristors only and there is a wider control over the level of dc output voltage. In this case, the average value of output voltage is given by V0= (2Vm/p ) cos a , where Vm=max. peak supply voltage and a is the firing angle. As such according to variation of a from 0 to p, the output voltage varies from (+ 2Vm/p ) to (-2Vm/p) . This is a two –quadrant converter where voltage polarity can reverse but current direction remains same. For firing angle 0 to p, power flows from ac source to motor load and is called rectifier operation of the converter. During the interval from p to (p+a) the load returns some of its energy to the supply system –this operation of full converter is known as inverter operation of the converter. Such an operation is used in the regenerative braking mode of a dc motor. A half-controlled converter or semi-converter uses a mixture of diodes and thyristors and there is a limited control over the level of the dc output voltage. In this case, mathematically, output voltage V0 = (Vm/p)(1+cos a). According to variation of a from 0 to p, the output voltage varies from 0 to (+2Vm/p).The output voltage never becomes negative i.e. it always acts in rectifier mode operation. This is a one –Quadrant converter where voltage and current polarity both remains positive throughout the operation. The PCB is designed for Full Controlled converter. The bridge end can be modified according to requirement-i.e. for semi controlled operation 2nos, Diodes and 2 nos. Thyristors are to be connected whereas for full controlled operation 4 nos. thyristors are to be used.

Pulse Inhibit Section:
The output pulses are blocked via pin6 of UAA145 by feeding +15V through normally close contact of main contractor. This is required to de-activate the pulse generator, when there is no ac voltage applied at the input of the thyristor bridge.

Regulator inhibit circuit:
The current and speed controller are inhibited by applying 0V at the input of FETs which are connected across the feedback section of the speed and current amplifier. When the main contractor is activated -15V is applied after about 470ms to the gate of n-channel FET to make it in OFF condition. The purpose of this is to restrict the output of the regulators (speed and current both) to 0 Volt during de-energized condition of the contractor.
dv/dt circuit:
The thyristor may get triggered without gate pulse, if the dv/dt of the incoming ac supply is more than the dv/dt capability of the thyristor, which is not desirable in practical case. To prevent it, snubber circuit is connected across each thyristor. Snubber circuit is series combination of R and C. It is only used for dv/dt protection purposes.

Panel:
The Drive is an electronic device. But to operate the drive, several external electrical connections are to be made with the externally fitted components such as reference potentiometer, actual feedback signal, Inhibit signal, armature and field connections, incoming ac voltages for control and power circuits separately, etc. The electrical circuits are to be designed /interlinked in such a fashion so that the sequence of operations is maintained properly for smooth operation. Different measuring meters, indicating lamps etc. are also fitted on the panel for visual indication of different parameters. The electrical circuit is prepared as per
fig.1 and fig. 2.

Claims:1) Claim for the design of Experimental setup for single phase thyristor controlled DC drive.[As per Fig.1 &Fig.2]
2) Claim for the design of PCB for layout no. LDRAB 001 as per circuit no. CDRAB 001 [Fig. 6]
3) Claim for design of PCB for layout no. LDRAB 002 as per circuit no. CDRAB 002{Fig. 8]
4) Claim for design of PCB for layout no. LDRAB 003 as per circuit no. CDRAB 003[Fig.3]
5) Claim for design of circuit for circuit no. CDRAB 001[Fig.5]
6) Claim for design of circuit for circuit no. CDRAB 002[Fig.7]
7) Claim for design of circuit for circuit no. CDRAB 003[Fig.4]
8) Claim for design of electrical inter-connection diagram as per Fig. no. 2 .