Electricity – HFAC Microgrid -
An interesting excerpt from telecommunication system papers, with a good description:
* * *
HIGH-FREQUENCY AC (HFAC) POWER DISTRIBUTION SYSTEM FOR TELECOMMUNICATION SYSTEMS
https://pdfs.semanticscholar.org/080c/e7de47eb8bc8d41d3ff28aea84ba2847c7b5.pdf
High-Frequency AC (HFAC) power distribution system was first proposed by NASA for space applications some 45 years ago [14], [15].
The HFAC power distribution approach offers several advantages over the conventional DC power distribution approach, which makes it an attractive solution for many applications such as telecommunications and computers.
The main advantage of HFAC power distribution is that the two main conversion steps are eliminated in the overall power distribution architecture [16].
The advantages of HFAC power distribution over conventional DC power distribution is given as:
- It is more efficient
- It is more reliable
- It has better heat distribution
- It has higher power density
- It also has the potential for connector-less power transfer.
Due to the above-mentioned significant advantages of the HFAC power distribution systems over the DC power distribution systems, HFAC power distribution is also being proposed for high-power density telecommunication as well as computer applications [17]. We have already seen that the conventional power distribution in telecommunication systems is based on the DC power distribution. DC power distribution is usually implemented using either the centralized architecture or distributed architecture. One of the main disadvantages of centralized DC power distribution is that due to the distribution of heavy current through the bus-bar, it creates a lot of losses and also requires a large amount of space on the backplane for tracking.
Also, remote voltage sensing is required to compensate for the voltage drops along the entire length of the cables. In addition, the heat generated by the DC-DC converters is very high and is mostly concentrated to the converter, which poses a great challenge to the management of thermal energy. Also, few DC-DC converters should also be used to provide redundancy, which can be considered as a necessary evil in the process of communication. Therefore, current sharing is necessary, which also brings complexity to the entire power distribution system [18].
Distributed DC power distribution architecture was introduced to overcome the setbacks due to the centralized DC architecture. This architecture utilizes the point-of-use power supplies (PUPS) in order to locally distribute power to the electronic cards in the telecommunication facility.
The main advantage of this architecture is that, there is a much more efficient thermal management due to the fact that heat is distributed throughout the entire system.
HFAC power distribution opens up a new horizon for telecommunication systems.
The HFAC distribution system not only combines the advantages of DC power distribution, but also offers newer features, which cannot be implemented in the DC power distribution systems alone. The main features of HFAC power distribution are listed as follows:
- It has excellent transient response since there is no low-pass filter (LPF) and HFAC feedback loop. - The AC power lines can also be used for communication, alarm triggering, etc.
- It has a very simple current limit circuit for the line feed.
- There is simplified insertion of electronic cards.
- It has a simplified ringing generator.
- It also has the potential for connector-less power distribution.
In this architecture, there is more than one DC-AC inverter in order to produce an HFAC sine-wave output, which is typically 60Vrms, with a carrier frequency of 128 kHz, from the battery voltage of -48V.
Then, the HFAC bus is distributed through the backplane to the electronic cards where AC PUPSs convert it to the required compatible DC voltages [19]. The HFAC bus in telecommunication systems can be of the voltage type or the current type.
The advantages of HF sinusoidal voltage distribution are that it has low electro-magnetic interference (EMI) and overall higher efficiency for a wide variety of loads.
A hybrid HFAC power distribution architecture was also proposed for the telecommunication systems in order to combine the advantages of both sinusoidal voltage and sinusoidal current distribution [20]. This hybrid HFAC architecture can provide the following features:
- It can be used for connector-less power transfer.
- It has fuse-less protection.
-There is sinusoidal voltage and current distribution.
- It has high overall system efficiency.
- In HFAC power distribution for telecommunication systems, several inverter modules are generally configured in parallel to provide reliable power distribution for several reasons, such as better heat dissipation, lower cost, elimination of short-time overload, provision of redundancy, better reliability, and designing of a modular structure. Even sharing of the power results in better thermal management, optimized component ratings, and thus, the overall cost is minimized [21], [22].
[posted for educational purpose only]
* * *
If you put together the above described system with those ones linked from our blog, and of course if you are 'awakened' and in knowledge, you will find it also as a neat path for application in other areas of interest, particularly in our Islands and Areas of Light.
Useful Links:
Control and Design of High Frequency Power Distribution System
http://jsaer.com/download/vol-1-iss-2-2014/JSAER2014-01-02-44-54.pdf
