Centralized monitoring of the power electronics devices

Centralized monitoring of the power electronics devices

This paper describes the solution for monitoring and control of power electronics devices in telecommunication facilities. Centralized monitoring of the power supply system enables monitoring of the operation of all devices in the system, using the same user application. In addition to monitoring of individual devices’ operation, the operation of passive elements, which together with the power electronics devices constitute the power system, is also monitored. With the implementation of derived alarms, such as organized, centralized monitoring increases the reliability of the power electronics system and enables the responsible sector to prevent interruptions in the operation of telecommunication equipment by preventive maintenance.

Managing power electronics devices represents switching on or switching off of monitored devices or modules, starting a capacitive test, and adjusting the operating parameters of the power supply device from the remote monitoring center. It is estimated that with such organized remote monitoring, the total costs of installation and maintenance of the power system can be reduced by 16%. The cost resulting from the interruption of telecommunication traffic as well as the cost of termination of the services due to the unreliable operation of the telecommunication system is not included in the savings’ calculation.

Remote Monitoring Technology (RMT) is one of the key factors for servicing the system. Although servicing has been the subject of intensive research for years, the role of RMT in this field is less explored. [1] Power systems consist of energy converters and elements that connect energy converters to energy sources and energy consumers.

Energy converters convert: •an alternating input voltage in direct output voltage (AC/DC converters), •a direct voltage of one value in the direct voltage of another value (DC/DC converters), •a direct voltage in alternating voltage (DC/AC converters – inverters). In addition to energy converters, the components of the power system are: •assembly of AC distribution: connects energy converters with alternating energy sources (power distribution network or generator), •assembly of DC distribution: Code Shoppy connects energy consumers with basic DC power sources and a spare power source (the most common accumulator). Energy converters and generators are complex devices and usually have a microcomputer which, in addition to monitoring the operation of the device itself, can also have the remote monitoring function.

On the other hand, AC and DC distributions consist of passive elements, so most often there is no monitoring of these elements’ operation. This practically means that it is a realistic situation that no one of the monitored devices sends an alarm to the monitoring sectors, regardless of the power system is defective. In practice, such cases are often noticed, and some of them have been described in previous papers [2-4]. The organization of the power electronics devices’ monitoring through the microcomputer, which is an integral element of energy converters, cannot supervise the power electronics system, but only certain elements. Another problem of the described monitoring approach is that microcomputers used for the control of power electronics devices are not a good solution for power electronics devices’ monitoring. Monitoring is not their basic function, so the data obtained in this way are not reliable. If the data are not reliable, the responsible sectors may make the wrong decisions. Figure 2 shows the shape of the voltage at the output of one AC/DC converter, for which the monitoring device showed that the DC voltage at the output of the converter is 190V, in the range of regular values (187V to 242V)

From the oscilloscope image, it is obvious that the DC voltage at the output of the converter changes within the limits of 50V to 300V and is beyond the permitted limits. The mean value of the voltage measured by the oscilloscope is the same as the value obtained using the microcomputer in the device (190V). However, the shape of the voltage shown on the oscillogram requires the urgent intervention of the monitoring sectors, while the data obtained from the microcomputer indicate that no intervention is needed. Another example is shown in Figure 3. The measurement was done with an oscilloscope with a probe that introduced a 10-drop attenuation on a serial resistor of 10 mΩ.

Practically, the current value per interval is 2A. An example is characteristic because no one monitoring device generates an alarm, no one size is beyond the range of allowed values. However, the system is not correct, because the existence of a large alternate component in the charging current of an accumulator suggests that there is a significant problem in the system operation. As a consequence, the operational autonomy of the spare power supply is significantly reduced.

The mean value of the charging current is within the allowed limits. However, there is an alternating component whose maximum value is greater than 8App. This means that there is a serious problem with the serial resistance between the charger and the accumulator. Resistance can be in the accumulator itself, but also in the connections between the charger and the accumulator. Also, the charger requires additional inspection, because the problem can be caused by large variations in the output voltage of the charger.

This problem does not require urgent intervention. However, if the serial resistance is the problem, the power system has no declared autonomy, and if the charger is the problem, the characteristics of the accumulators will be degraded. It is necessary to inspect the operation of several elements of the power supply system. In order to detect the problem of this type, a serious analysis of the collected data obtained from the monitoring systems, as well as the appropriate expert knowledge and experience in the monitoring sectors, is required. By installing remote monitoring and control systems for power electronics devices – SDNU, it is possible to collect the required data set to help analyze the operation of monitored devices. One solution is to automatically generate messages from monitoring programs that would suggest to monitoring sectors what to do. Such messages are named derived alarms [3].

For the described example, the derived alarm would announce a reduced power supply autonomy and suggest that a capacitive test must be done. Both of the above-described examples were recorded after the installation of a device that has been developed specifically for the monitoring of power electronics devices. A mounted centralized monitoring device recognized the alarm state and generated alarms, but local monitoring of the energy converter did not recognize the alarm state. Due to no match in the measurement results, the competent maintenance sectors requested a determination of the right status. Oscilloscope records confirmed that the only correct solution for monitoring of power electronics devices is the use of a device that has been specifically developed only for the monitoring and control of power electronics devices. Accumulator monitoring systems are also independent systems that have the battery life prediction function based on ambient temperature and the discharge curve monitoring. The battery status is transferred to the operating center to increase the reliability of the power supply. [5] The monitoring centers collect data from microcomputers located in the power electronics devices. The usual solutions are that each energy converters’ manufacturer develops its own monitoring system to monitor the operation of the energy converter. The application software has been written so that only one type of energy converters and from only one manufacturer can be monitored at one point in time. This means that different power electronics devices of different manufacturers cannot be monitored simultaneously on the same monitor. This is not a good solution for maintenance sectors, because while monitoring the operation of one type of device, there may be some major accidents on some other devices. In order to avoid this situation, it is common practice to have a large number of monitors in the maintenance sectors, to monitor the operation of each type of power electronics device. Such a solution is not appropriate, because due to poor transparency, it is really possible that some of the alarms pass unnoticed. There are also standardized protocols (SNNP) that allow monitoring of the different devices’ operation on one monitor, but the data set is limited and used in the main (national) monitoring centers. In these centers, there are no experts dealing specifically with the maintenance of power electronics devices, so it is impossible to perform an analysis of the complete system operation. The data collected through standardized protocols are used to engage responsible maintenance sectors based on receiving alarms, in order to intervene on the object in alarm. In this case, there is no possibility of preventive maintenance, but only corrective maintenance. From the data collected through standard protocols, the cause of the alarm is not visible, but the existence of an alarm is noted and this information is forwarded to the maintenance sectors. In practice, it is common that after obtaining an intervention order, and after going on-site, the responsible maintenance sectors find that they cannot correct the defect, because it is not caused by the operation of the power electronics devices in their jurisdiction.

The paper describes one solution for the organization of remote monitoring and control of power electronics devices. The described solution is optimized for maintenance sectors. All elements in the power electronics system are monitored so that the state of each circuit in the system is reliably known. Data from the microcomputer are also collected if they exist as integral elements of the power supply system. In the monitoring center, all data are displayed on one monitor. In order to improve the efficiency of the maintenance sector, the data are divided into three levels. With monitoring organized in this way, the maintenance sectors, in addition to receiving the alarm from an object, can also determine the cause of the alarm and decide who and when to intervene, in order to eliminate the alarm. In addition to reducing the unnecessary going on-site of the maintenance team, the planned maintenance of the power supply system elements is enabled. It is estimated that with such organized remote monitoring, the costs of servicing and replacing elements in power electronics systems can be reduced by about 60%. Savings are achieved due to the extension of the life of spare power supplies about 27%, as well as due to a reduction of the traveling cost assigned to the maintenance sectors of 34%. The cost resulting from the interruption of telecommunication traffic as well as the cost of termination of the services due to the unreliable operation of the telecommunication system is not included in the savings’ calculation. After ten years of tracking the power systems’ operation and analyzing the data obtained from the remote monitoring and control system SDNU, the above data have collected. This assessment coincides with the assessment of some other companies, such as “MIDTRONICS-Battery Management Innovation”, made for Telecommunication companies in the USA Click Here