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SCM MPPT Charge Controller Consisting Of The Basic Principles

Author: Source: Datetime: 2016-09-14 16:15:29
This is a block diagram of the charge and discharge controller with MPPT function, due to their relatively complex circuit, there is no longer provide specific application circuit, portable solar power generator comes from the A/D conversion function microcontroller (MCU), the voltage acquisition circuit, a current acquisition circuit , DC/DC conversion circuit. Technically mainly controlled by a microcontroller and software acquisition, composition measurement circuit, DC/DC converter circuit of three parts.

The technical requirements of the specific terms of each part as follows.

①DC/DC converter circuit - generally from BUCK or BOOST type circuit type, ask for a higher conversion efficiency above 85% or 90%, but low-power DC/DC circuit efficiency is relatively low, only 60% of 75? %. Thus, the controller has MPPT function in the following 50WP PV system advantage is not obvious, rarely used, but mainly used in larger systems. There is also a problem of matching system design and PV module power DC/DC converter circuit, the load size to match, so the system is near capacity, more efficient Wei Gao. DC/DC converter circuit has a boost (BOOST), buck (BUCK) type, buck (BUCK and BOOST) type, according to the specific choice of what kind of PV module voltage, battery voltage and load the operating voltage is determined.
② measurement circuit main DC/DC converter circuit of the input side of the voltage and current value, the voltage value of the output side, in addition to temperature measurement circuit M. Measuring circuit requiring a simple and reliable measurement accuracy to meet the technical requirements of the withdrawal, from the product point of view there should be a high cost performance.
③ Microcontroller monitoring software and chip technology has developed rapidly in recent years, a variety of low-power single-chip multi-functional efficiency Gao lot, is also a great range of choice, such as INTEL 80C196 has sine wave output, PHILIPS companies P87LPC7G7 as with A/D conversion of compact low-power products, etc. there is also a single chip instead of using the DSP controller. To achieve the MPPT function, monitoring software is very important, what kind of control algorithm of the effect varies widely, such as commonly used algorithms are: constant voltage tracking method, perturbation and observation method, the incremental conductance method, standard lifePo4 battery look-up table method, not detailed here introduction, section 5.3 discusses the left.
The controller must have several basic functions

The solar power portable generator system charge and discharge regulation and control is an important function of photovoltaic application systems. Small system, you can use a simple system to achieve controllers for medium and large PV systems can also be used include a set of functions g more sophisticated control devices set to achieve. Apart from a small system (such as general solar lamps, etc.) and applications for consumer products, the charge controller used in the PV power plant system must have several of the following basic functions:
① anti-battery charge function;
② anti-battery discharge function;
③ provide load control function;
④ provide system status information to the user operator functions;
⑤ provide backup energy control interface functions;
⑥ PV systems can provide surplus energy consumed by the load to the auxiliary function;
⑦ provides interfaces (such as monitoring) function.

And several developers need to pay attention to the optional controller problem

Several basic functions mentioned above, namely: anti-function battery overcharge, over discharge, anti-load short-circuit functions endures, there are several important indicators.

① from the power controller itself is lower. In particular, has become an important indicator in the application of small systems, the World Bank standards from the current consumption is less than 1% of the rated current, so choose low-power device design and circuit is very important,
② circuit voltage drop lower. World Bank standards is a circuit voltage drop should be less than 5% of the system voltage, which is closely associated with the design and selection circuit switching device.
③ anti-PV components or reverse battery protection. In between the battery negative terminal of the lifePo4 batteries positive and connected in series with a high-power diode fuse.
④ anti-anti-charge protection. In the solar cell anode input end in series reverse charge diode or other switch-mode battery current backflow prevention.
⑤ lightning protection. If the PV system is installed in a place vulnerable to lightning in the controller input side and connected varistors or other additional lightning protection measures.

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