MAX: Making reference to a MPPT controller stating to be digital and doing the voltage testing by opening the load is a system that for hydro would be unreliable,
One can use analog or digital techniques to do MPPT without the need to present an open line (load) to the generator and for the systems I have done opening the load is NOT good. The power of small systems produces a Bell shape power form from stalling to open loaded for wind mills and hydros, as well as, solar panels. For under-load MPPT tracking, one needs to set a load current variation to the time constant behavior of the system to permit the generator to respond to the current changes reflecting power changes and power curve direction without the need of opening the load. The summation of input voltage, output voltage and current with the proper insertion parameters plus a time constant do an accurate job for MPPT to obtain from 20 to about 30 % increase in power harvesting. -- FOR SOLAR, WIND , HYDRO. Since MPPT is not well understood by quite few "installers" is not used or used in a wrong way, for this reason many use the wrong equipment or the wrong setup to optimize the harvesting of power. As an example: people using wind mills that clamp the output of the generator to the battery voltage that at peak power the generator has to absorb sometimes more then 50 % of the generated power and the battery takes what is left = about 50 %. With MPPT the wind mill will generate its high voltage well above the battery voltage and the controller converts this power to the battery voltage, in this case, instead to just using 50 % of the available power, the battery bank will be able to harvest 75 to 85 + % of the generated and available power in the system. For Small Hydro systems to attain the same results, where the power generation, time constant is quite longer one needs to use some other techniques. In Microhydro systems one needs to understand that MPPT has to exist in one of several forms for proper power output -- ONE needs to understand the all systems -- Wind, Hydro, Solar, HAVE TO HAVE MPPT . Now that I called your attention: MPPT to the LOAD or MPPT to the GENERATOR needs to exist. MPPT to the LOAD : the Load is varied to Harvest the peak power available MPPT to the GENERATOR : the Generator is Varied to Harvest the energy PEAK that the LOAD requires In the MPPT to the LOAD case, the generator may have very limited power capability, much less than the load can Harvest. In the MPPT to the GENERATOR case, the Generator may have greater power than the load can Harvest. Quite few installers do not determine the time constant of the system, though easy to determine, usually it is not done or it is done via brute force HOPING that the controller can do it; the ELC controllers that I have designed have had the circuit that I called (Hydro constant = analog) for smooth power regulation and control. So, to finish here, open circuit testing is not needed -- at any time -- open circuit was implemented because it was easier to implement digitally -- but completely unwanted.and BAD for Wind and Hydro, OK for solar due to the output voltage limitations. Regards Nando ----- Original Message ----- From: "Max Enfield" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, June 21, 2005 6:15 AM Subject: Re: [microhydro] MPPT for turbines > tajuddin waris wrote: >> >> Dear >> All member >> >> As we know that MPPT (maksimum power point tracking) have been used in PV >> and wind turbine in order to improve efficiency the whole system. Is >> there any research application of MPPT for microhydro particularly >> microhydro driving small turbine like pump as turbine ? >> >> regard >> >> waris > > > In previous postings to this group I have stated that I gave up counting > once > our accumulated experience using what are now called AERL Hydromax > controllers > exceeded 50 years. The Hydromax controller is a modified Maximizer used > for > MPPT of PV arrays. The main modification is that the automatic tracking > feature > has been disabled and a manual adjustment used instead. It has proved > itself to > be an excellent, flexible, efficient and robust arrangement that we have > used > many times. The Hydromax controller is placed between (in an electrical > sense) > the DC hydrogenerator and a lower voltage DC load, which is usually a 12V, > 24V > or 48V battery. > > The method is suitable only when the turbine/generator can be freewheeled > and so > this typically limits the method to low and medium head sites. We have > successfully used this approach for Banki-crossflow, Turgo, Pelton wheel > and > Aquair UW propellor turbines. A novel application is undergoing trials in > southern NSW (Australia) on a large travelling irrigator. Some of the > water > delivered under pressure to the irrigator passes through a propellor > turbine and > an AERL Hydromax controller is used to control the generation of > electricity > required for on-board use. > > Any MPPT device requires a real time algorithm to determine the MPP. With > AERL > units this is done once every 25 seconds by momentarily allowing the input > to go > to open circuit voltage and then bringing this voltage down until there is > no > further improvement in output. This is OK for PV but with micro-hydro it > presents at least two difficulties. Firstly it induces an unpleasant > voltage > spike and secondly the spinning reserve of the turbine/generator defeats > the > controller's efforts to determine OC voltage within the few milliseconds > time > frame it allows itself. This is why a manual adjustment is used. > > It may at first appear that manual setting of the MPP defeats the benefits > of > automatic tracking that has proved so useful for PV. However this is not > so and > although the reason is not straightforward, I will try to explain it > simply. > > As the head and flow characteristics of a turbine site vary, due to the > season > or rainfall level, usually it is the flow rate rather than the head that > changes > dramatically. It is unusual for the net head to vary by more than 30% > above or > below some average value. The output voltage characteristics of a > generator > depend only on the net head and hardly at all on the flow rate. > Furthermore, > any > change in net head results in proportionately a much smaller change in the > MPP > - only about half as much. For example a 30% increase in net head will > increase > the MPP voltage by only 14%. > > An additional stabilizing factor is that at the maximum power point the > power > curve is rather flat. So operating a few percentage points either side of > this > point causes only a small reduction in output. Using the above example, > if the > MPP voltage is 14% above the operating voltage the reduction in output is > barely > 2%. So, for all practical purposes, the reduced efficiently due to manual > rather than automatic setting of the MPP is tiny. > > The relationship between head variation and reduced efficiency involves a > quartic polynomial. If anyone is interested in the formula they can > contact me > directly. > > Regards, > > Max Enfield > Planetary Power > www.planetarypower.com.au > > > > > > Does your company feature in the microhydro business directory at > http://microhydropower.net/directory ? If not, please register free of > charge and be exposed to the microhydro community world wide! > > NOTE: The advertisements in this email are added by Yahoogroups who > provides us with free email group services. The microhydro-group does not > endorse products or support the advertisements in any way. > > More information on micro hydropower at http://microhydropower.net > > To unsubscribe: send empty message to > [EMAIL PROTECTED] > Yahoo! Groups Links > > > > > > > Does your company feature in the microhydro business directory at http://microhydropower.net/directory ? If not, please register free of charge and be exposed to the microhydro community world wide! 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