A Novel Noninvasive Failure-Detection System for High

450 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 60, NO. 2, FEBRUARY 2013 A Novel Noninvasive Failure-Detection System for High-Power Converters Based on SCRs Victor Guerrero, Student Member, IEEE, Jorge Pontt, Senior Member, IEEE, Juan Dixon, Senior Member, IEEE, and Jaime Rebolledo, Student Member, IEEE Abstract—In modern high-power industrial processes, multi- The new method presented in this paper consists of a series pulse cycloconverters are fundamental to feed synchronous mo- of algorithms which is capable of giving a detailed information tors. Given the importance of these critical processes, particularly about the failure that occurred in the cycloconverter, processing for mining industry, the reliability of the high-power drive is critical. Having a noninvasive system capable of detecting and isolating only the values of input and output currents of the converter (the faults in the thyristors is quite valuable, and it will reduce the noninvasive feature of the method). Although, in this paper, this economic losses caused by the long repair times of the converter. method is presented for the 12-pulse cycloconverter without Currently, it is difficult and, in some cases, almost impossible circulating current, it is important to say that this detection to determine which of the SCRs experience an overcurrent or system works for any multipulse cycloconverter. those which do not trigger properly, causing a malfunction. In this paper, we present a new method of online detection which This paper shows, in detail, the operation of the 12-pulse is capable of delivering information about the SCR involved in a cycloconverter based on SCRs (Section II), showing the power failure and the nature of it. This new method takes only a few input circuit, firing-pulse-generation method, and the free cirulating and output measurements (noninvasive feature) already available current configuration of the system. in the most of industrial cycloconverters and performs a timing Section III shows all the theoretical bases of two very analysis of these measurements. The algorithms of the method es- timate and analyze the switching states of all thyristors, providing important algorithms in the fault-detection system: switching- an impressive way of detecting the cause and consequences of the state-estimation and fault-detection algorithms. Finally, in failure in the cycloconverter. Section IV, it presents the simulation and experimental test Index Terms—Diagnostics, drive, fault tolerance, industrial ap- under fault conditions which verify the diagnosis capability of plication, reliability. the fault-detection system. I. INTRODUCTION II. THE 12-PULSE CYCLOCONVERTER N THE LAST few decades, the field of high-power drives WITHOUT CIRCULATING CURRENT I has shown a great development mainly because all industrial processes have been increasing their power demand to achieve a Synchronous motors are the preferred solution for high- large-scale economy [1], [2]. The high-power drive applications power mills [4], and cycloconverters are one of the most include pumps and compressors (petrochemical industry), lami- common ways to feed them. That is why a lot of research has nators (metal industry), trucks and ships (transportation), active been made to propose methods to improve the power quality of filters, high-voltage direct current and wind power conversion these systems [5], [6], mitigating harmonics and interharmonics (energy industry), etc. [19]. present on these drives [7]–[9]. In the mining industry, the use of multipulse cycloconverters This section discusses the simulated and built cycloconverter to feed semiautogenous grinding mills is quite common [3]. that was used for the testing process of the detection system Because of this, it is necessary to have monitoring and fault- proposed in this paper. detection systems capable of delivering an accurate and fast diagnostic of any failure that occurred in the converter, reducing A. Power Circuit the economic losses due to a long repair process. The electrical diagram of the 12-pulse cycloconverter with- Manuscript received December 2, 2010; revised May 14, 2011 and out circulating current is shown in Fig. 1, where the presence December 21, 2011; accepted January 1, 2012. Date of publication February 16, of four rectifier bridges in every phase (each one with six 2012; date of current version September 13, 2012. This work was supported SCRs) can be seen. There are two groups of bridges connected in part by the CONICYT-Chile Project 1100988, by the Chilean Millennium Scientific Initiative under Grant P07-087-F, and by the Universidad Técnica in parallel, “the positive bridges” and “the negative bridges,” Federico Santa María, Valparaíso, Chile. each one is composed of two bridges in a series. “The positive V. Guerrero, J. Pontt, and J. Rebolledo are with the Universidad Técnica bridges” carry the positive cycle of the load current, and the Federico Santa María, Valparaíso 2390123, Chile (e-mail: victor.guerrerob@ alumnos.usm.cl; [email protected]; [email protected]). other group is active only when the load current is negative. J. Dixon is with the Department of Electrical Engineering, Pontificia Univer- Table I shows all the construction and simulation parameters sidad Católica de Chile, Santiago 8331150, Chile (e-mail: [email protected]). of the converter, which were used for the diagnostic tests of the Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. failure detection system. These parameters are based on typical Digital Object Identifier 10.1109/TIE.2012.2188251 requirements for these types of drives [10]. 0278-0046/$31.00 © 2012 IEEE GUERRERO et al.: NOVEL NONINVASIVE FAILURE-DETECTION SYSTEM FOR HIGH-POWER CONVERTERS 451 Fig. 1. Twelve-pulse cycloconverter. TABLE I DESCRIPTION OF THE SIMULATED AND BUILT CYCLOCONVERTER B. Firing Pulses Considering the one-phase equivalent shown in Fig. 2, four different firing signals can be identified. The α1 and α2 signals are related to the “positive bridges,” and the α3 and α4 signals are the ones which carry the firing angle of the “negative bridges.” This differentiation in the signals given to the cycloconverter is the basis of the free circulating current mode, where the two groups of bridges never work at the same time. The relationship between the firing angle α and the average output voltage (see Fig. 2) of each bridge of the system is given by Vout = vm cos(αi) (1) where Vout represents the average output voltage of the bridge associated with the firing-pulse signal αi and vm is a propor- tional value to the voltage amplitude of the input in the bridge, which can be the line–line voltage of the secondary delta or star depending on which secondary the bridge is connected to. III. SWITCHING-STATE-ESTIMATION AND FAILURE-DETECTION SYSTEM High-power cycloconverter-fed gearless motor drives experience a series of current and failure issues [11]; that is why it is very important to have an intelligent monitoring and an Fig. 2. One-phase equivalent. 452 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 60, NO. 2, FEBRUARY 2013 (see Fig. 2) with one of the 12 switching cases of the normal operation; see Table II. It is also possible to establish the currents in each primary of the power transformers with the currents through the secon- daries of the transformers using the following equations: N2Y N2Δ ia = (iaY − ibY )+ iaΔ (2) N1 N1 N2Y N2Δ ib = (ibY − icY )+ ibΔ (3) N1 N1 N2Y N2Δ ic = (icY − iaY )+ icΔ (4) N1 N1 where ia, ib, and ic represent the currents through the primary of the transformer; iaY , ibY , and icY are the currents through the secondary star; iaΔ, ibΔ, and icΔ are the currents through the secondary delta; N2Y /N1 represents the ratio of the number of turns between the primary and the star secondary; and N2Δ/N1 represents the ratio of the number of turns between the primary and the delta secondary. If the equations that relate the currents in the primary and secondary of the transformers are available and the currents in Fig. 3. Switching sequence. the secondary in the normal operation of the CCV can only take − accurate diagnosis system to overcome these difficulties [12]. values as iload, iload, or zero depending on the switching state This section shows the way the fault-detection system works of each SCR (where iload represents the current through the and gives the theoretical bases of its functioning. connected load in the analyzed phase), it is possible to construct The detection system consists of a series of algorithms that a table that relates a normal switching case with a particular runs in parallel for the three phases of the cycloconverter. They relationship between primary and load currents (see Table III). For calculation reasons, it is considered that the relations of measure the ia, ib, and iload of the phase being studied; these currents are defined in Fig. 2. The system delivers information turns in the windings of the transformers allow an identical about the switching state of every SCR and the nature of line–line magnitude voltage in the primary delta and secondary any fault that occurred in the analyzed phase. If this method delta. is implemented for the three phases of the cycloconverter, it The main function of the switching-state-estimation algo- is possible to establish the switching state of any of the 72 rithm is to take the numerical values of the currents in the SCRs of the cycloconverter (CCV), as well as the possibility primary and the load of each phase, compare the relationship of detecting a failure in the CCV and the nature of it. between them using Table III, and delivering information about The failure detection system consists of four stages. The first the switching case presented in the CCV.

Load more