Electric power conversion systems – Current conversion – Having plural converters for single conversion
Reexamination Certificate
2001-01-19
2001-07-17
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Having plural converters for single conversion
C363S070000
Reexamination Certificate
active
06262900
ABSTRACT:
The invention relates to controlling the operation of power supply systems in general. In particular, the invention relates to controlling the modules of such a modular power supply system, in which a centralized control unit can make the modules operate at different voltage levels by commands.
FIG. 1
depicts a prior art modular power supply system
100
, which is used to feed battery-backed electric power to the load. The system comprises N parallel power units, of which only
101
and
102
are shown in the figure for clarity. The positive integer N is generally selected such that even if one power unit failed, the performance of the remaining power units would be sufficient to meet the power requirement of the load in normal circumstances. The power units are rectifier and control units, the inputs of which are connected to alternating current (AC), which is generally a common electricity distribution network. The outputs of the power units are connected to the load
103
. The power units can be called the modules of the system.
In order to ensure uninterrupted power supply, the system includes a storage battery
104
, which is connected in parallel with the load by means of the equipment
105
, which prevents deep discharge of the battery. The latter is essentially a switch, which cuts the supply of electricity from the storage battery to the load when required, and thus prevents a complete discharge of the storage battery in a situation in which the power units have been unoperational for some time, and the charge of the battery has been mostly discharged to the load. The operation of the system is controlled by a control unit
106
. In order to implement data transfer between the control unit and power units, the system has a data transfer connection
107
, which can be a serial bus, for example. In the following, the data transfer connection between the control unit and the power units is generally called a serial bus, regardless of how the connection has been implemented in a practical embodiment. The data transfer connection between the control unit
106
and the equipment
105
which prevents deep discharge of the battery, can be implemented through the same serial bus or there can be a separate connection for it, which is independent of the serial bus.
Measurements of the condition of the storage battery
104
often require that the battery is discharged at times. For this, the output voltage of the power units
101
,
102
is lowered to a so-called support level. After the measurement, the storage battery must be fully charged again, for which the output voltage of the power units
101
,
102
is raised back to the permanent charge level or to a somewhat higher quick charge level. Quick charge is used particularly if the discharge of the storage battery has taken a long time. After some time, the output voltage of the power units must be lowered to the permanent charge level in order to prevent the overvoltage from damaging the storage battery or the load. Regulating the output voltage to the support level, permanent charge level or quick charge level takes place so that the control unit
106
gives an output voltage regulation command to each power unit via the serial bus
107
. The regulation commands are numeric values or encoded commands, which are converted into numeric values in the power units.
In addition to the centralized output voltage regulation, the system comprises selective overvoltage control, which is implemented separately in each power unit. The selective overvoltage control interrupts the operation of the power unit in question, if the output voltage of the power unit exceeds a certain predetermined overvoltage limit. Selectiveness means that the operation of the power unit is only interrupted if the power unit is loaded in an overvoltage situation, that is, current is detected at its output simultaneously with an output voltage which is higher than the overvoltage limit. The operation of the selective overvoltage control in a certain power unit is not dependent on other power units.
The reliability of a system according to
FIG. 1
is substantially weakened by the possibility of a common-mode failure. This means that the operation of at least two power units is disturbed by a common cause simultaneously and in the same way. Generally, the reason for this is that the control unit has given the wrong command, as a result of which the output voltage of all power units is too low or too high and/or it remains at the wrong level for too long a time.
It is an objective of the present invention to provide a method and equipment for controlling the operation of a system comprising power units in such a manner that the probability of a common-mode failure is small. It is also an objective of the invention that the manufacturing costs of the construction are low.
The objectives of the invention are achieved by saving certain criteria in the power units, on the basis of which criteria the power units can determine whether the control command given by the control unit is sensible. The operation of the power units is arranged such that they do not execute a control command which does not meet the saved criteria.
The method according to the invention is characterized in that it comprises steps in which
the control unit gives a control command to the power unit,
the power unit examines whether the control command received by it meets certain predetermined and saved criteria, whereby
a control command which meets the saved criteria is executed, and
a control command which does not meet the saved criteria is not carried out.
The invention also relates to a modular power supply system, which is characterized in that it comprises means in each power unit for saving criteria that determine the rationality of the control commands, and means for comparing the received control command to the saved criteria.
According to the invention, the operation of a modular power supply system comprises a configuration mode and an operation mode. In the configuration mode, certain criteria are saved in each power unit, by means of which criteria the power unit can determine whether the control command received by it is sensible. The saving is called the configuration of the power sources, and it is carried out in a situation in which it is clearly known what each command given by a control unit means and what each value contained in the command refers to. The configuration can be carried out under the supervision of an electrician, for example. In the operation mode, the power units receive control commands from the control unit in the same way as in the prior art system, but instead of executing the commands without questioning, each power unit compares the command received by it to the criteria saved in connection with the configuration and executes only the commands which are sensible as compared to the criteria.
Suitable criteria include the numeric value of the level of each output voltage (permanent charge level, support level, quick charge level etc.) and the duration of an output voltage level which differs from the permanent charge level. The power unit checks whether the output voltage level referred to by the control command meets the level of the criterion, and for how long the command referring to an output level voltage which differs from the permanent charge level has been in force. If the output voltage level referred to by the control command contradicts the saved criteria, or if an output voltage level which differs from the permanent charge level has continued longer than the criterion allows, the power unit returns its output voltage to the permanent charge level or interrupts its operation.
According to the preferred embodiment of the invention, certain factory settings or limiting values have been fixed in the programmable parts of the power units or at the “hardware” or component level, which factory settings function as criteria for the criteria used by the system. It is not possible for the user to save a criterion which would violate the factory settin
Greenberg & Traurig, LLP
Muuntolaite Oy
Sterrett Jeffrey
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