APPLICATION NOTE 004

Daisy Chaining DISO UNITS

By Benjamin Bacon, Owner, Plane Space Design

A group of DISO units can be connected together to form an electrical power system that has many Inputs but only one Output. This would be useful when a lot of different sources of electrical energy are available but not all at the same time; each being available at its own somewhat random time. This is one example of when daisy chaining of the sources to a single Output may be beneficial. In doing so the redundancy of the power source system is increased. There are some other reasons for daisy chaining that produce useful results that can be achieved by that type of connection of DISO units. In this application the purposes for daisy chaining that are relevant to the management of renewable energy sources are considered.

There is no limit to the number of sources that may be connected to a system of DISO units to form a single daisy chained power system. No matter what number of units are required to be connected there are some properties of the DISO that makes this an easy task. First, the enclosure of the DISO unit is built upon the standardized PVC pipe system. Therefore there are a vast number of fittings available to aid in the connection strategy. The coupling fittings that enable two DISO units to be joined end-to-end or side-by-side will be most useful . The DISO units require fittings that are made for 3 inch PVC cylinders. The internal diameter of the DISO unit's cylinder is about 3 inches and the outside diameter is about 3.5 inches.

Another simplifying feature is the circumferential placement of the Inputs and Output on each DISO unit. By rotating one unit 90 degrees with respect to the other, one of the Inputs of one DISO unit is in line with Output of the other DISO. Why this is convenient will become apparent shortly.

When DISO units are daisy chained, one possible connection scenario has the Output of one unit connected to one of the Inputs of the next. To aid the description of connections, the units can be labeled by numerical indicators of where a particular DISO is positioned in the system as shown in Figure 1 below. Let  DISO unit one be the DISO unit whose power Output will be used to connect to a load to be driven by the power complex.  Call this DISO unit stage one of the power complex. Another DISO unit connected to the one end of stage one will be stage two, and the unit connected to the free end of stage two is stage three and so on. This type of labeling helps to describe how the system is to be wired and where each DISO unit is positioned

.

For simplicity a power complex with two stages will be described. A 3 inch PVC couple can be placed between stage two and stage one to join them together. The Output of one stage connects to the Input of another. When an Output is connected to an Input they are connected with the positive terminal of the Output connected to the positive terminal of the Input and the negative terminal of the Output connected to negative terminal of the Input. That is the basic idea of daisy chaining.

At this point it must be decided which Input of stage one the Output of stage two will connect to. The choices of terminal connections are, the Output of stage two connects to the Main Input of stage one or the Output of of stage two connects to the Secondary Input of stage one. This choice, combined with the choice of what sources are connected to the Main and Secondary Inputs of stage two determines how the power complex will behave and what happens at the Output of stage one, where the power is taken for use.  Daisy-chaining is simple but it is not trivial. There are a lot of ways the power can be transferred from three sources to a load in this set-up.

Certain properties of a daisy chained DISO power complex can be discussed. First, there can be N + 1 sources connected to a complex where N is the number of stages used. The last stage in the complex, stage N, has two free Inputs while all of the other stages have one free Input, since one Input of these other stages is used to connect to the Output of the next stage. For example for a two stage complex, N=2. The last stage is N = stage 2 and this stage has has two free Inputs. Stage one has one free Input since the Output of stage two connects to one of the Inputs of stage one. There can be N + 1, equals three, sources connected to a two stage complex.

In a daisy chained DISO power complex, the power from only one source can get through to the Output of stage one; (The exception to this rule is a DISO power complex made up of current sharing DISO units only). When using DISO units that perform Exclusive OR on the sources, (that is DISO units that are NOT configured for current sharing), only one of the sources in the complex propagates to the stage one Output. To try to describe general rules for how this happens is complicated, but this can be more simply done on a case by case basis.

Consider a complex where the Output of each stage is connected to the Secondary Input of the next lower stage. Based upon the way that a DISO operates, the voltages connected to the Main Inputs of every stage has the best chance of making it to the Output of that stage if the Main voltage is sufficient but there is no way it will go to the Output of the next lower stage unless the Main voltage of that next lower stage drops out; and it will require the voltages on the Main Inputs of all the lower stages to drop out for a source to reach the Output of stage one. In other words, any voltage that tries to propagate down to stage one, must compete with the Main voltage of all the lower stages between its stage and stage one. A propagating source must win at every stage to get to stage one and this only happens when the Main voltages at every stage between this source and stage one have all become insufficient, including the Main voltage at stage one. On the other hand, the closer a voltage source is to stage one, the better its chances of making it to the stage one Output, all things being relatively equal at every stage. The exception to this rule for DISO units programmed for switching at fixed voltage levels is the case where all  of  the voltages on the complex somehow become equal to each other. In this case they will all provide approximately the same amount of current to the Output of stage one. That is one Nth of the total current.

When the complex is made from current sharing DISO units, the situation is different. It is possible for every source in the complex to contribute to the current output at the first stage. This happens when all of the sources connected to the DISO power complex are at the same voltage. The only time that no voltage appears at the stage one Output in the current sharing DISO complex is when all of the sources have failed to produce at least the minimum voltage that a DISO unit requires to operate.

The last possibility in daisy chaining is when the types of DISO units in the power complex are mixed. There needs be a lot of forethought put into constructing something like this. In fact, every DISO power complex requires a great deal of forethought in considering what source connects to which stage so that the power coming out at stage one is somewhat predictable.

Summary

In this application note the meaning of daisy chaining of DISO units was described. Some of the properties of a daisy chained power complex made from DISO units were discussed. A system for describing DISO unit power complexes was presented. In this system each DISO unit connected to the chain is called a stage. Stage one is the end unit where the Output terminal will connect to a load that the power complex will provide power for. Each additional stage will add one to the size of the complex. The last stage is designated stage N, where N is the number of DISO units used. The number of sources that can be connected to a complex using N DISO units  is N + 1.  Some of the possible electrical behavior of a DISO power complex was postulated. However behavior could not be exactly described because it is dependent upon a lot of factors such as the type and number of the DISO units used in a complex and the types of power sources that connect to the Inputs at each stage. The description and discussion of a DISO power complex is handled best by analyzing them on a case by case basis. Complete generalization of electrical behavior is not possible for the daisy chaining application of the DISO units.