All language subtitles for [LANG] How a VFD or variable frequency drive works - Technical animation [DownSub.com]

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Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:00,000 --> 00:00:02,700 The conveyor belt is driven by three 2 00:00:02,700 --> 00:00:05,490 phase AC motors. How is it possible that 3 00:00:05,490 --> 00:00:07,890 this line can start and stop so smoothly? 4 00:00:07,890 --> 00:00:10,889 Let's have a look at the control - it's 5 00:00:10,889 --> 00:00:12,870 all because of the frequency converter. 6 00:00:12,870 --> 00:00:18,990 Other common terms for this electronic 7 00:00:18,990 --> 00:00:22,320 device used in drive technology are VFD, 8 00:00:22,320 --> 00:00:24,570 known as variable frequency drive, 9 00:00:24,570 --> 00:00:28,439 adjustable frequency drive or AC drive 10 00:00:28,439 --> 00:00:31,560 converter. With this device you can 11 00:00:31,560 --> 00:00:34,380 control speed torque and direction of an 12 00:00:34,380 --> 00:00:37,380 AC motor at the same time. So let's know 13 00:00:37,380 --> 00:00:40,829 this device better. This block diagram 14 00:00:40,829 --> 00:00:42,750 illustrates a typical three-phase AC 15 00:00:42,750 --> 00:00:45,059 variable speed drive system with its 16 00:00:45,059 --> 00:00:48,239 main components: First the incoming AC 17 00:00:48,239 --> 00:00:50,670 voltage enters a bridge rectifier which 18 00:00:50,670 --> 00:00:54,090 consists here of 6 diodes. In this stage 19 00:00:54,090 --> 00:00:57,570 the DC voltage has ripples. Therefore a 20 00:00:57,570 --> 00:00:59,579 capacitor and a filter helps to smooth 21 00:00:59,579 --> 00:01:03,239 out the ripple. Now the DC bus system can 22 00:01:03,239 --> 00:01:06,510 take its place. The filter DC bus voltage 23 00:01:06,510 --> 00:01:09,090 passes through to a DC three-phase AC 24 00:01:09,090 --> 00:01:14,040 converter: The DC/AC converter consists 25 00:01:14,040 --> 00:01:15,900 of an array of fast-acting switches, 26 00:01:15,900 --> 00:01:17,939 which convert the DC voltage into 27 00:01:17,939 --> 00:01:20,670 voltage pulses of square shape and constant 28 00:01:20,670 --> 00:01:23,549 magnitude with varying width. The inverter 29 00:01:23,549 --> 00:01:26,460 output is not a truth sine wave but an 30 00:01:26,460 --> 00:01:29,700 approximation based on pwm or pulse 31 00:01:29,700 --> 00:01:32,670 width modulation. This pulse width 32 00:01:32,670 --> 00:01:34,560 modulation scheme works because the 33 00:01:34,560 --> 00:01:36,689 motor coils are large inductors, which 34 00:01:36,689 --> 00:01:38,640 does not allow current to pulse like the 35 00:01:38,640 --> 00:01:39,760 voltage. 36 00:01:39,760 --> 00:01:42,160 To ensure the efficient operation of the 37 00:01:42,160 --> 00:01:44,440 motor, the sine waves produced by each 38 00:01:44,440 --> 00:01:47,050 pair of inverted switches are 120 39 00:01:47,050 --> 00:01:50,080 degrees out of phase. The longer the 40 00:01:50,080 --> 00:01:52,240 switches are on the higher the output 41 00:01:52,240 --> 00:01:54,790 voltage. This way you can control the 42 00:01:54,790 --> 00:02:00,250 torque of this motor regarding the speed 43 00:02:00,250 --> 00:02:02,230 of the motor by increasing the frequency 44 00:02:02,230 --> 00:02:04,720 of the output signal. You get a higher 45 00:02:04,720 --> 00:02:07,630 number of revolutions but now you have a 46 00:02:07,630 --> 00:02:10,180 problem: The inductive reactance of the 47 00:02:10,180 --> 00:02:12,040 motor coils rises by the signal 48 00:02:12,040 --> 00:02:14,560 frequency. That means you would get less 49 00:02:14,560 --> 00:02:17,410 torque. So what is the solution to 50 00:02:17,410 --> 00:02:20,800 overcome this obstacle? You would adapt 51 00:02:20,800 --> 00:02:22,570 the voltage to the frequency when 52 00:02:22,570 --> 00:02:25,540 acceleration and deceleration. The 53 00:02:25,540 --> 00:02:27,850 parameter called ramp describes the 54 00:02:27,850 --> 00:02:30,610 voltage frequency ratio. The other 55 00:02:30,610 --> 00:02:33,370 parameter boost also known as the torque 56 00:02:33,370 --> 00:02:35,950 compensation is to compensate the torque 57 00:02:35,950 --> 00:02:37,959 decrease in low speed because of the 58 00:02:37,959 --> 00:02:39,640 stator winding resistance of the 59 00:02:39,640 --> 00:02:41,950 electric motor and the starting torque 60 00:02:41,950 --> 00:02:45,400 caused by friction. The base edge 61 00:02:45,400 --> 00:02:47,380 frequency is achieved when the voltage 62 00:02:47,380 --> 00:02:49,330 supplied to the motor reaches the main 63 00:02:49,330 --> 00:02:52,510 supply voltage. Raising the frequency 64 00:02:52,510 --> 00:02:54,430 above the edge frequency leads to 65 00:02:54,430 --> 00:02:56,440 magnetic saturation which cannot be 66 00:02:56,440 --> 00:02:59,530 compensated anymore. As a result the 67 00:02:59,530 --> 00:03:02,890 torque of the motor decreases. Concerning 68 00:03:02,890 --> 00:03:04,480 the technical implementation of the 69 00:03:04,480 --> 00:03:06,790 inverter: As electronic switches 70 00:03:06,790 --> 00:03:10,540 transistors are used. In this case IGBTs. 71 00:03:10,540 --> 00:03:13,780 In order to avoid a short-circuit their 72 00:03:13,780 --> 00:03:16,239 control connections are interlocked. The 73 00:03:16,239 --> 00:03:18,610 diodes serve as a freewheeling diode 74 00:03:18,610 --> 00:03:23,010 since the motor coil is an inductance. 5615

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