Hydro Systems Using LCBsª Paul Cunningham An inherent problem of hydro systems is their site specific nature. With a wind or PV system the situation is different. The same sun shines everywhere and the same air blows around. With wind and PV you can always add more equipment to harness more power. With hydro, every site is different and there is usually limited water. Conditions Most hydro machines will only perform well under certain conditions and only perform at their best under one set of conditions. Using a variable field, as with automotive alternators, is one solution. These machines can be used with an RPM range of around 1000 to 4000 or more. Although these alternators are low in cost and fairly reliable, they have low efficiency, typically 50% or less, depending on conditions. So with variable field strength, controlled electronically or with a rheostat, an optimum match between input power and output power can be made. Improving the situation Let's look at some ways of improving the situation. The automotive alternators have a place. But at low-head sites they work poorly or not at all. The problem is made worse because they not only are less efficient at low speeds, but more power is required to operate the field as the speed (head) is reduced. The only practical solution is a generator that uses permanent magnets (PM) for the field. This can be done using either stationary magnets with a rotating armature like DC motors have, or the rotor can contain the magnets with the armature and its coil of wire being stationary. Either way, the permanent magnets supply the magnetic flux that moves in relation to the output coils (where the power is generated). This is free of charge, no energy is added to produce the magnetic field. Thus gains in efficiency are possible, and the machine can also operate at very low heads. Half Solved This is a step in the right direction, but the problem is only half solved. The field strength must be controlled (or some other techniques used) to produce optimum output. One way is to custom build each generator for each site (ARGH!). Another is to mechanically adjust the distance of the magnets from the armature (ARGH again!). In the case of stationary coils and PM rotors, it is possible in some designs to reconnect the output coils to vary the loading. But even so, this cannot be done in small increments. And I won't even discuss mechanical drives like belts and pulleys for these very small machines. This is because of their complexity and losses. Wouldn't it be nice Wouldn't it be nice if this could be done electronically so one machine could be used at widely differing sites? There are devices called Maximum Power Point Trackers that do this. They automatically seek out the best operating point of a power source and effectively match the power power source to the load . The only ones I know of are very expensive. We aren't going to benefit if the operation is successful but the financial strain kills the patient. A Buck Regulator Several years ago I built a similar device, called a buck regulator, that could track the power point. A transistor controlling the power is simply switched on and off and the pulsed electric current flow is smoothed by an inductor, see Figure 1. A higher voltage is converted to a lower one with minimal losses. Although this device worked, I never commercially produced the buck regulator. LCBs Recently, I used a standard LCBª (linear current booster) made by Bobier Electronics (type 3-4-8-T) with a permanent magnet, DC hydro machine and had excellent results. This machine (model DCT-1) could charge a 12VDC battery with a five foot head. I wanted to operate it at a 15 foot head. This meant that if the PM generator was connected directly to the battery it would run too slowly and the power output would decrease. The PM generator would produce a higher power output if the generator could turn faster which meant operating the system at a higher battery voltage. The optimum voltage increases in proportion to the speed of the PM generator. Easily Retrofitted An LCB can easily be retrofitted to a hydro site. If you have a PM generator, or in some cases an induction machine, you may benefit. With a PM generator, if the no-load voltage exceeds twice the battery voltage, a performance increase is possible. The installation of the LCB is very simple. It should be installed according to instructions as if it were operating in a PV system, see Figure 2. The LCB should be mounted near the battery bank. Then it can simply be adjusted for maximum output current. At the 15 foot head site, the no load voltage was around 47 VDC. This meant that the correct voltage under load should be about 23 Volts. By using a variable resistance, I determined that the maximum power point was at 22.l VDC and 2.1 Amperes giving 46.4 Watts. Connecting the generator directly to a 12 VDC battery produced 3.0 Amperes and 12.5 VDC or 37.5 Watts. This is about 81% of the maximum that was produced at 22 VDC. Using the LCB in the circuit produced an output of 3.6 Amperes at 12.6 VDC giving 45.4 Watts. This means the efficiency of the whole system, with the LCB is around 98%. It is important to note that the power increases will rise as the difference between generated voltage and battery voltage increases. LCBs are available from Bobier that are rated up to 250 VDC. Other Benefits There are other benefits from using an LCB. Whenever nozzles are changed, the machine can easily be re- adjusted for maximum performance. Another plus is that the generator voltage is increased which greatly reduces transmission line losses. Bobier has just introduced new models of LCBs. Devices specifically designed for use with batteries must be ordered. Access Paul Cunningham, Energy Systems & Design, POB 1557, Sussex, N.B. Canada E0E1P0 ¥ 506-433-3151 Bobier Electronics, 800-222-3982