1 00:00:05,490 --> 00:00:07,299 Welcome back. 2 00:00:07,299 --> 00:00:13,110 Now we come to an important power electronic device that makes the battery storage in the 3 00:00:13,110 --> 00:00:15,139 modern PV system widely applicable. 4 00:00:16,260 --> 00:00:18,640 I am talking about the charge controller. 5 00:00:19,540 --> 00:00:23,880 What is a charge controller, and why do we need it? 6 00:00:23,890 --> 00:00:29,970 Note that the use of charge controllers is found in PV systems with battery usage. 7 00:00:29,980 --> 00:00:35,040 In most cases, this would mean a stand-alone PV system. 8 00:00:36,300 --> 00:00:42,540 In the previous video about the battery parameters, you have learnt the importance of having the 9 00:00:42,540 --> 00:00:47,440 right amount of current and voltage being provided to the battery. 10 00:00:48,820 --> 00:00:55,420 You know that the battery is an electrochemical device which requires a small over-potential 11 00:00:55,430 --> 00:00:56,950 when it needs to charge. 12 00:00:57,620 --> 00:01:04,700 However, battery technologies have strict voltage limits required for their optimal functioning. 13 00:01:05,140 --> 00:01:11,719 Also, the amount of current sent to the battery by the PV array and the current being discharged 14 00:01:11,719 --> 00:01:18,719 away by the load have to be within required limits for proper functioning of the battery. 15 00:01:20,979 --> 00:01:27,240 You have also seen previously, how a lead-acid battery responds poorly to overcharge 16 00:01:27,240 --> 00:01:28,400 and overdischarge. 17 00:01:29,539 --> 00:01:38,800 You also know how the PV array responds dynamically to ambient conditions like irradiance, temperature 18 00:01:38,800 --> 00:01:40,500 and other factors like shading. 19 00:01:41,700 --> 00:01:48,700 Under such circumstances, a direct coupling between a PV array, battery and load is far 20 00:01:48,700 --> 00:01:51,600 from healthy for the battery. 21 00:01:51,600 --> 00:01:58,600 This means that we need a device that can interface 3 way - between the PV system, 22 00:01:58,740 --> 00:02:06,060 the battery and the load, and ensure that the electrical parameters around the battery are 23 00:02:06,069 --> 00:02:10,809 maintained within the battery manufacturer's specifications. 24 00:02:12,760 --> 00:02:15,440 This is where the charge controller comes in. 25 00:02:16,230 --> 00:02:21,230 The modern charge controller performs a multitude of functions. 26 00:02:21,860 --> 00:02:27,540 These functions can further be enhanced depending on the set of technologies the manufacturer 27 00:02:27,540 --> 00:02:31,240 wishes to integrate within the device. 28 00:02:32,860 --> 00:02:35,940 I will discuss the most basic functions here. 29 00:02:37,000 --> 00:02:43,880 When the sun is shining in peak summer, there is enough PV energy meeting the load. 30 00:02:43,890 --> 00:02:46,670 The excess energy is sent to the battery. 31 00:02:47,380 --> 00:02:53,680 But when the battery is fully charged, and the PV array is still connected to the battery, 32 00:02:53,690 --> 00:02:55,950 the battery tends to overcharge. 33 00:02:56,780 --> 00:03:02,560 This brings about its own set of problems like gas formation in the lead-acid battery, 34 00:03:02,570 --> 00:03:06,030 capacity loss and overheating, to name a few. 35 00:03:07,480 --> 00:03:13,860 The charge controller here plays a vital role by cutting off the PV power from overcharging the battery. 36 00:03:14,910 --> 00:03:20,980 Similarly, in severe winters when low irradiance causes the load demand to be more than the 37 00:03:20,980 --> 00:03:25,220 supply power, the battery is heavily drawn. 38 00:03:26,820 --> 00:03:32,740 The battery under such conditions tends to be overdischarged, which weighs strongly 39 00:03:32,740 --> 00:03:36,180 on the battery life, as discussed in the previous block. 40 00:03:37,470 --> 00:03:43,270 The charge controller under such a case prevents overdischarge by disconnecting the battery 41 00:03:43,270 --> 00:03:44,090 from the load. 42 00:03:46,400 --> 00:03:52,680 For optimal performance, the battery voltage has to be within specified limits. 43 00:03:52,690 --> 00:03:58,820 The charge controller can help in maintaining an allowed voltage range so as to ensure a 44 00:03:58,820 --> 00:04:00,770 healthy operation. 45 00:04:00,770 --> 00:04:08,900 Also, the PV array could have its Vmpp at different levels, based on the temperature 46 00:04:08,900 --> 00:04:11,540 and irradiance conditions. 47 00:04:11,540 --> 00:04:17,989 Therefore the charge controller needs to do an appropriate voltage regulation to ensure 48 00:04:17,989 --> 00:04:26,029 the battery operates in the specified voltage range, while the PV array functions at MPP. 49 00:04:27,180 --> 00:04:34,460 This means that the modern charge controller can, and often does, integrate an MPP tracker 50 00:04:34,680 --> 00:04:36,140 within its design. 51 00:04:37,920 --> 00:04:42,280 We have seen before how the battery has certain C-rates defined. 52 00:04:43,340 --> 00:04:50,020 Higher the charge/discharge rates, the lower the coulombic efficiency of the battery will be. 53 00:04:51,300 --> 00:04:57,860 The optimal charge rates indicated by the manufacturer could be adhered to by manipulating 54 00:04:57,860 --> 00:05:00,420 the current flowing into the battery. 55 00:05:02,460 --> 00:05:08,080 With proper current regulation, the charge controller is also able to control the C-rates. 56 00:05:08,800 --> 00:05:14,419 At the very least, the charge controller can impose the limits on the maximum allowable 57 00:05:14,419 --> 00:05:18,219 currents flowing into and from the battery. 58 00:05:19,460 --> 00:05:25,660 Without blocking diodes, it is even possible that when the PV array is producing a very 59 00:05:25,669 --> 00:05:32,620 low voltage, the battery can load the PV array, or in other words, the battery can try to 60 00:05:32,620 --> 00:05:38,779 forward bias the PV modules and make them consume the battery power. 61 00:05:38,779 --> 00:05:45,400 Traditionally, blocking diodes are used at the PV panel or string level to prevent the 62 00:05:45,400 --> 00:05:49,860 supposed "back discharge" of the battery through the PV array. 63 00:05:51,560 --> 00:05:57,200 This function is also easily integrated these days via the charge controller. 64 00:05:58,380 --> 00:06:04,940 I won't go into too much of the hardware details but most charge controllers usually have either 65 00:06:05,110 --> 00:06:08,610 a shunt or a series kind of controller. 66 00:06:10,240 --> 00:06:16,920 In a series controller, the overcharging is prevented by cutting out the PV array until 67 00:06:16,930 --> 00:06:22,990 a particular voltage drop is detected, at which point the circuit is completed again. 68 00:06:24,249 --> 00:06:29,939 On the other hand, in a parallel or shunt controller, the overcharging is prevented 69 00:06:29,939 --> 00:06:31,959 by shorting the PV array. 70 00:06:32,480 --> 00:06:38,900 This means that the PV modules work under short-circuit mode, and that no current flows 71 00:06:38,909 --> 00:06:39,929 into the battery. 72 00:06:41,500 --> 00:06:48,439 These topologies also ensure over-discharge protection using power switches for the load 73 00:06:48,439 --> 00:06:53,559 connection, appropriately controlled by the charge controller's algorithm. 74 00:06:54,189 --> 00:06:59,539 We have seen in the previous block how the temperature plays a crucial role in the functioning 75 00:06:59,539 --> 00:07:01,559 of the battery. 76 00:07:01,559 --> 00:07:07,779 Not only does temperature affect the lifespan of the battery, but it also changes its electrical 77 00:07:07,779 --> 00:07:09,559 parameters significantly. 78 00:07:10,889 --> 00:07:14,719 How does the charge controller handle this situation? 79 00:07:14,719 --> 00:07:21,719 A good charge controller these days comes with an in-built temperature sensor. 80 00:07:21,749 --> 00:07:27,949 Therefore, it compensates for temperature fluctuations and dynamically decides how the 81 00:07:27,949 --> 00:07:32,729 electrical specifications like operating voltage change with temperature. 82 00:07:34,020 --> 00:07:40,020 It successfully keeps the battery operating in the desired range of voltages, depending 83 00:07:40,029 --> 00:07:40,989 on the temperature. 84 00:07:42,700 --> 00:07:48,620 For this reason the charge controller is usually kept in close proximity to the battery, 85 00:07:48,620 --> 00:07:53,960 so that the battery's operating temperature is close to that of the charge controller. 86 00:07:55,260 --> 00:08:01,560 In extreme cases, if the battery is heavily loaded, sustained high currents might heat 87 00:08:01,569 --> 00:08:06,839 up the battery, and the charge controller would expect a different battery operating 88 00:08:06,839 --> 00:08:09,559 temperature than the actual value. 89 00:08:12,580 --> 00:08:18,180 However, high-end charge controllers are being designed to also take into account the temperature 90 00:08:18,509 --> 00:08:21,419 effects due to high currents. 91 00:08:21,419 --> 00:08:27,619 This space of developing application specific power electronics for PV systems is evolving 92 00:08:27,619 --> 00:08:29,559 at a very high pace. 93 00:08:29,559 --> 00:08:35,250 Thus, the charge controller can go a long way in increasing the lifespan of the battery 94 00:08:35,250 --> 00:08:40,090 by ensuring a healthy battery operation under most conditions. 95 00:08:41,320 --> 00:08:47,260 The modern charge controller has become an indispensable part of the stand-alone PV system. 96 00:08:47,940 --> 00:08:53,800 Like any other component of the PV system it is expected to have a very high efficiency. 97 00:08:54,560 --> 00:09:00,800 I have given you an overview of this very important power electronic device in this block. 98 00:09:02,000 --> 00:09:07,520 This week has been about knowing the various components of your PV system. 99 00:09:07,529 --> 00:09:13,709 In the next and the last week of the course, I would show you how these components come 100 00:09:13,709 --> 00:09:20,190 together and create different types of PV systems, and what are the basic things to 101 00:09:20,190 --> 00:09:24,680 be kept in mind before designing your PV system. 102 00:09:25,160 --> 00:09:26,880 So, see you in the last week!