IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 30, NO. 3, JUNE 2015
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Power Component Fault Detection Method and Improved Current Order Limiter Control for Commutation Failure Mitigation in HVDC Chunyi Guo, Member, IEEE, Yuchao Liu, Chengyong Zhao, Member, IEEE, Xiaoguang Wei, and Weihua Xu
Abstract—A power component detection (PCD) method and an improved current order limiter control (improved COL) are proposed to mitigate the commutation failure in a line-commutated converter-based high-voltage direct current (LCC-HVDC). Integrating the instantaneous voltage and instantaneous current characteristics under single-phase and three-phase-to-ground faults, a fault detection method based on the power component is proposed, and the corresponding setting principle is presented. Then, an improved dc current order limiter is introduced. To evaluate the effectiveness of the proposed methods, a dual-infeed HVDC system is developed in PSCAD/EMTDC, and the presented methods are also implemented. The transient performances of dual-infeed HVDC, under single-phase and three-phase-to-ground faults at the inverter ac busbar of one LCC-HVDC link, are investigated. Simulation results show that the PCD method, with the voltage and current components as an additional judgment criterion, is more sensitive to detect the single-phase and three phase faults, and even more reliable than the detect method taking only voltage or current components for faults recognition. It can also be concluded that the improved COL that is integrated with the advancing firing angle control has the ability to make the LCC-HVDC less susceptible to commutation failure. Finally, the improvement of commutation process by improved COL is further demonstrated. Index Terms—Commutation failure, improved current order limiter, LCC-HVDC, power component detect.
I. INTRODUCTION
L
highINE-COMMUTATED-CONVERTER-BASED voltage direct current (LCC-HVDC) has been wildly applied to many areas, such as asynchronous ac grid connection, long distance bulk power transmission, etc.. However, if the short-circuit ratio (SCR) of an ac network is low, the
Manuscript received August 14, 2014; revised January 29, 2015; accepted March 05, 2015. Date of publication March 24, 2015; date of current version May 20, 2015. This work was supported in part by the National High Technology Research and Development Program of China (863 Program) under Grant 2013AA050105, in part by the National Science Foundation of China under Grant 51177042, in part by the Specialized Research Fund for the Doctoral Program of Higher Education under Grant 20130036120006, and in part by Major Projects on Planning and Operation Control of Large Scale Grid of State Grid Corporation of China under Grant SGCC-MPLG004-2012. Paper no. TPWRD-00990-2014. C. Guo, Y. Liu, and C. Zhao are with the State Key Laboratory for Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China (e-mail:
[email protected]). X. Wei and W. Xu are with the State Grid Smart Grid Research Institute, Beijing 102200, China. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPWRD.2015.2411997
LCC-HVDC system would have poor voltage regulation ability and be susceptible to commutation failures (CFs) [1]. The CF issues can be alleviated by synchronous condenser (SC), static synchronous compensators (STATCOM) or voltage-source-converter-based HVDC (VSC-HVDC) [2]–[5], all of that can supply the dynamic reactive power for LCC-HVDC. However, more extra capital costs are required for additional apparatus to CFs mitigation. There is also a lot of valuable literature on fault detection, CF recognition, and CF mitigation by the control system. A method to calculate the maximum-allowable balanced voltage drop at an inverter ac busbar is given to determine the CFs onset [6]. However, it was deduced based on a three-phase balanced voltage drop, and fast transient events were not considered, sometimes resulting in inaccuracy for CF determination. A new index, called the commutation failure immunity index (CFII), is proposed to quantify the immunity of an LCC-HVDC converter to CFs [1]. The voltage-dependent dc current order limiter (VDCOL) is widely used in LCC-HVDC systems to reduce the CFs probability and improve fault recovery performances. A voltage-dependent dc voltage order limiter (VDVOL) is presented to reduce the CFs probability for a VSC-LCC-type hybrid HVDC system [7]. However, it is not suitable for LCC-HVDC. Reference [8] presents a method to calculate the necessity of advancing firing pulses, which shows the favorable ability to avoid CFs. References [9]and [10]develop fuzzy controllers to minimize the CFs effects on the LCC-HVDC transformation and system. Reference [11]adopts the abczero-sequence voltage for three-phase and single-phase faults detection, respectively. Thus, the method relies on the reliable monitoring for the ac instantaneous voltage. Then, the output value from the inverter firing control is deduced to advance the firing angle and mitigate the CFs. With the presented method, the favorable results are obtained. However, with the increase of the commutation margin, the reactive power consumption of the inverter is also increased. Based on further investigation of commutation processes and commutation failure mechanisms, a dc predictive control strategy is proposed to inhibit CFs [12], and favorable results are obtained. However, the transmission delay of the dc current order from the inverter to rectifier should be further considered to investigate the presented controllers. In this paper, the power component detection (PCD) method and its setting principle are presented to detect the single-phase and three-phase faults, which are the most frequently occurring unbalanced faults and the most serious faults. The PCD
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equivalent capacitance of the filters and compensator; system-equivalent impedances of the receiving ac system. Fig. 1. Schematic diagram of LCC-HVDC.
From Fig. 1, the following equation can be deduced: (1)
method integrates both instantaneous voltage and instantaneous current characteristics. Then, an improved current-order limiter (improved COL) control, integrated with advancing firing angle control, is presented to further mitigate the CFs. A dual-infeed HVDC system, with the proposed PCD and improved COL embedded, is developed in PSCAD/EMTDC. The characteristics of the PCD method and the CF probability in dual-infeed HVDC with improved COL control are investigated under the single-phase and three-phase faults condition. The results show that the PCD method, with the voltage and current components as an additional judgment criterion, is more sensitive and more reliable to detect the single-phase and three-phase faults than that of the method just considering the voltage or current component. Moreover, the improved COL has the ability to reduce the risk of CFs.
(2) where inverter. If (1) and (2)
, and is the advanced firing angle of the is the firing delay angle, then . From
(3) (4) just has a slight change initially caused by Suppose that some disturbance and the firing delay angle will decrease to mitigate the CFs, then (5)
II. ANALYSIS OF ADVANCING FIRING ANGLE CONTROL Under low ac voltage conditions or with a sudden increase in the dc current, LCC converters are susceptible to CFs. An offgoing valve in the LCC is said to have commutated successfully if the transfer of current from it to the next ongoing valve is completed. If this fails to happen, and the offgoing valve continues to conduct or spontaneously turns on when forward biased, a CF is said to have occurred [1]. Recently, the advancing firing angle control is widely used in LCC-HVDC projects to mitigate the CFs when faults occur. It will provide a certain margin for thyristors to accomplish the commutation process. Generally, it will reduce the probability of CFs. However, the method may have some negative impact on successful commutation of LCC-HVDC. Fig. 1 shows a schematic diagram of LCC-HVDC. The system parameters are defined as follows: ,
,
,
,
,
, ,
,
(6) is decreased, will increase. Considering , will also rise up based on (5), which has a negative impact on successful commutation. Meanwhile, the power factor angle will also change, resulting in reactive power imbalance, which will affect the value of . Equations (7) and (8) can be easily obtained After
(7) (8) Based on (3), (7), and (8), take the partial derivative of with respect to , then (9)
real and reactive powers of the rectifier and inverter;
(10)
dc voltages of the rectifier and inverter, and dc current;
(11)
electromotive force (emf) of the receiving ac system;
(12)
line-to-line voltages at the ac busbar of the rectifier and inverter; transformer leakage reactance of the rectifier and inverter; transformer turns ratio of the rectifier and inverter;
From (10) and (12), , . Considering that the ac system should have enough short-circuit capacity, then based on (11). Thus, it can be easily obtained from (9) that will also decrease with advancing the firing angle control. In conclusion, when advancing firing angle control is activated due to voltage drop from the ac system, the dc current will increase and ac voltage at the receiving side will decrease, which both potentially partially reduce the CFs immunity of
GUO et al.: POWER COMPONENT FAULT DETECTION METHOD AND IMPROVED CURRENT ORDER LIMITER CONTROL
LCC-HVDC. Thus, it may have some negative impact on successful commutation of LCC-HVDC. Especially at some special circumstances, for example, the advancing firing angle control has a slight impact on the commutation area of the offgoing valve in the process of turnoff; meanwhile, the increased dc current may further lead to the unsuccessful commutation for the offgoing valve, and finally induces the CFs. III. PCD METHOD AND IMPROVED COL CONTROL If the rise of dc current can be limited after the ac system fault is detected, the advancing firing angle control would play a larger role in CFs mitigation. The dc current order limiter control can be utilized to limit the rise of dc current, and one of that is the voltage-dependent current order limiter (VDCOL). The dc voltage at the rectifier side can be obtained by (13) where
. From (3) and (13) (14)
Suppose that just has a slight change initially, when the firing delay angle increases, which is induced by the dc current order limiter control under the receiving-side ac fault condition, then (15) From (2),
can be obtained by (16)
will be on the downward trend, which will From (15), also potentially decrease the dc current, with the increase controlled by the dc current order limiter. The real power at the inverter side can be calculated by (17) According to (7), (8), and (17), take the partial derivative of with respect to , then (18) (19) (20) (21) Based on (21), it can be easily obtained that 0. Considering that the ac system should have enough short-circuit capacity, then from (20). According to the system operation states, especially the values of , , and , can be obtained from (19). Thus, it can be easily obtained from (18)
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that will have an increasing trend with the dc current order limiter control. In conclusion, if there is an ac voltage drop at the receiving side due to some fault, compared with the advancing firing angle control, the current order limiter control has the ability to potentially decrease the dc current and increase the , which both potentially strengthens the commutation failure immunity of the LCC-HVDC. However, the dc current rise induced by faults cannot be limited immediately after the fault occurs. There are a few key factors influencing how fast the dc current rise can be limited: 1) faults detect delay, which can be minimized by a more sensitive detect method; 2) dc current order transmission delay from the inverter to rectifier, which cannot be avoided; and 3) the dc current drop rate is mainly determined by the smoothing reactor and dc current order drop rate, etc. A. Analysis of VDCOL VDCOL has been widely used for LCC-HVDC projects. When the dc voltage drop or ac voltage drop due to some fault is detected, dc current order will be decreased and then transmitted to the rectifier side, which is helpful for LCC-HVDC to mitigate the CFs and improve the system recovery performances. However, there is a milliseconds delay to measure the dc voltage and ac voltage rms values; thus, the dc voltage drop or ac voltage drop are not sensitive enough to be obtained, which will slow the rate of dc current decreases. In addition, the dc current order of VDCOL changes with the dc voltage in a linear relation, in which way the dc current cannot be reduced quickly. Thus, dc current has a slow drop rate when the VDCOL is activated. B. PCD Method The characteristics of instantaneous voltage are adopted to detect the single-phase and three-phase faults [11], which can be improved to detect the fault more quickly. According to the analysis from before, a more sensitive fault detection method is important for CFs mitigation. If the fault can be quickly detected, further control can be quickly carried out to mitigate the CFs. Here, a PCD method, which is power component detection, is presented in order to achieve faster and more sensitive detection for single-phase and three-phase faults than that in [11], which integrate the instantaneous voltage and instantaneous current characteristics. Based on the measured ac busbar instantaneous voltage, that is, , , , and instantaneous current, that is, , , , the absolute values of the zero-sequence voltage component and current component can be calculated by (22) (23) And the rotation vector amplitudes of voltage and current in the - plane can be obtained as the following equations: (24)
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Fig. 3. Control diagram of the proposed method.
Fig. 2. Diagram scheme of the PCD method.
(25) (26) (27) where and are the component and component of the voltage rotation vector in the - plane, and and are the and components of the current rotation vector in the plane. Then, the zero-sequence power component and the power component deviation in the - plane are defined as follows: (28) (29) and are the maximum zero-sequence Suppose that voltage and current components at the normal operation state, the rated value of , namely, can be easily obtained by putting , into (28). In (29), and are the rotation vector amplitude of rated voltage and rated current. Generally, the acceptable ac voltage deviation range is within 5% of the rated value. If is assigned a value of , and is assigned a value of the rotation vector amplitude of current under the maximum load condition, then put the two values into (29) and the rated value of , namely, , can be obtained. The and will be the threshold values for fault judgment. Without any fault, and are very small and close to 0. The diagram scheme of PCD is shown in Fig. 2. The voltage component and current component detected under the fault condition are also adopted as the additional judgment condition to make the power component detection more accurate. As shown in Fig. 2, , , , , , and are the reliability coefficients of , , , , , , respectively, which are all threshold values.
When the fault occurs, , , , will experience a sudden change, and and will have more obvious fault features. When , , and , the single-phase to ground fault is detected; when , and , the three-phase-to-ground fault is detected. With appropriate design for the reliability coefficients, the PCD method will have more favorable characteristics than other detection methods, taking only voltage or current characteristics under the fault condition into consideration. The setting principles of , , , and for voltage and current components can follow that of overcurrent protection. Considering that and will increase under the single-phase-to-ground fault, and should be larger than 1, and could be at a range of 1.2~1.3. Similarly, considering that will decrease and will increase under the three-phase to ground fault, could also be at a range of 1.2~1.3, while should be smaller than 1 and could be assigned a value of 0.95, as is the acceptable lower limit of ac voltage per-unit value under the normal state. For PCD, and should also be larger than 1, but a relatively larger value in order to ensure no misjudgment for single-phase and three-phase faults. It is noted that if just voltage or current components are adopted as the judgment criterion, the larger values of , , and a smaller value of should be assigned to ensure no misjudgment for the faults by sacrificing their margins. However, the voltage and current components are utilized just as an additional judgment condition of the proposed PCD method, and , , and can be smaller, and can be larger. Thus, combing the characteristics of voltage, current, and power components under the fault condition, the proposed PCD method will be more sensitive and more accurate, which will be verified by the case study in Section IV-A. C. Proposition of an Improved COL Control According to the analysis in Section III-A, dc current has a slow drop rate when VDCOL is activated under the fault condition. In this paper, after the fault is detected by the PCD method, an improved current order limiter (improved COL) control, adopting a step-down current order, is presented to reduce dc current quickly and leave more commutation margin. With a smaller current order , dc current will decline more rapidly. However, should not be set to a very small value. If the is set to a very small value, the LCC-HVDC will lose high-power output. Here, an alternative approach is presented and the corresponding control diagram is shown in Fig. 3.
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TABLE I PARAMETERS OF LCC-HVDC1
Fig. 4. Diagram scheme of a dual-infeed HVDC system.
The procedures of the improved COL control are as follows. 1) When a single-phase or three-phase-to-ground fault is detected by the PCD method, the dc current order is stepped down to and , respectively. The PCD method focuses more on rapidity and accuracy of fault detection in order to react to the fault as soon as possible, rather than the evaluation of the fault severity. Considering a few factors, such as the overvoltage capability of the smoothing reactor, the improvement of the commutation process by reduced dc current, etc., under a single-phase fault condition could range from 0.75 to 0.85 p.u., and under a three-phase fault condition could range from 0.7 to 0.8 p.u. 2) In order to make LCC-HVDC not lose higher power output in procedure (1) under the situation that LCC-HVDC would not suffer from the CFs when just a slight fault occurs, supplementary control should be considered. Here, the current order will be set to a ramp increase, once the real power at the inverter side is smaller than the power lower limit under a single-phase fault, or in a three-phase fault. Considering the acceptable power loss under the instantaneous slight fault condition, the limit value of can range from 0.6 to 0.7 p.u., and can range from 0.55 to 0.65 p.u. 3) Thereafter, the VDCOL will also be activated, and a minimum dc current order will be selected between the VDCOL and the improved COL for LCC-HVDC system recovery from the fault. Based on the aforementioned three procedures, dc current under fault condition can be more effectively limited compared with VDCOL. Meanwhile, the power loss can be reduced to a smaller range, which will be demonstrated in the following section. It should be noted that the improved COL is presented not to replace the advancing firing angle control, but to collaborate with it and make the advancing firing angle control play a better role for CF mitigation. IV. SIMULATION ANALYSIS To evaluate the effectiveness of the proposed PCD method on single-phase and three-phase faults, and the improvement of the CFs immunity for LCC-HVDC by improved COL, a dual-infeed HVDC system, as shown in Fig. 4, is developed in PSCAD/ EMTDC. In Fig. 4, the LCC-HVDC1 is rated at 800 kV and 8000 MW, and the LCC-HVDC2 is rated at 500 kV and 3000 MW. Both LCC-HVDC links operate in constant current control
TABLE II PARAMETERS OF LCC-HVDC2
mode at the rectifier side and constant extinction angle control mode at the inverter side, as in the CIGRE HVDC Benchmark model [13]. The transmission tie line between two LCC-HVDC links is 100 km, and its parameter is km [14]. The other parameters are shown in Tables I and II. A. Investigation of the Proposed PCD Method Supposed that one outgoing line of the inverter ac busbar of LCC-HVDC1 has unbalanced three-phase loads , , and , and the sensitivity of the proposed PCD method is investigated under two types of ac faults at the outgoing line: 1) single-phase-to-ground fault with 0.17 H grounded and 2) three-phase to ground fault with 0.24 H grounded, respectively, as shown in Fig. 4. Both faults occur at 2.0 s and last 50 ms. The simulation results under single-phase and three-phase faults in PSCAD/EMTDC are given in Fig. 5(a) and (b), respectively. Since the fault location is close to LCC-HVDC1, only a few concerned electric parameters in LCC-HVDC1 are shown in Fig. 5. From Fig. 5(a), the zero-sequence voltage component rises up to 6 times the threshold value , and the zero-sequence current component rises up to 8 times the threshold value within 2 ms after the single-phase-to-ground fault. However, based on the proposed PCD method, the zero-sequence power component calculated by (13) will increase to approximately 50 times the threshold value within 2 ms after fault. Similarly, from Fig. 5(b), the amplitude of the voltage rotation vector drops to 93% of the threshold value , and the amplitude of the current rotation vector rises up to 2.5 times the threshold value within 2 ms after the three-phase-to-ground fault. Suppose that the ac current under maximum load condition is 1.1 times the rated current, when the
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Fig. 5. Investigation of the PCD method under single-phase and three-phase faults.
proposed PCD method is utilized, the power component deviation , calculated by (14), will increase to approximately 25 times the threshold value . In Fig. 5, the threshold values of , , , , , and are also plotted. Here, the threshold crossing time is defined as the time interval from the fault time to the threshold crossing point. From the results, although the time will get longer along with reliability coefficients increase their margins, the zero-sequence power component and the power component deviation in the PCD method will be more sensitive than the individual instantaneous voltage or instantaneous current under fault conditions. In addition, a larger margin for each reliability coefficient will be required to ensure no misjudgment for fault detection under some situations; then, the advantages of the PCD method will be better shown. In conclusion, the presented PCD method as in Fig. 2, with the voltage and current components as an additional judgment condition, is more sensitive to detect the single-phase and threephase faults, and even more reliable than the detection method in taking only voltage or current components for fault recognition.
B. Investigation of the Presented Improved COL The CFII index is adopted here to evaluate the susceptibility of the LCC converter to CFs and it is defined as in (30) [1] Critical Fault MVA
(30)
The CFII is determined by conducting a sequence of EMT simulations, each with an inductive fault applied to the converter bus. The Critical Fault MVA is the strength of the most severe fault that the tested system can survive without experiencing any CFs. is the dc power of the converter. The larger CFII value represents stronger immunity of the LCC inverter to CFs. To evaluate the effect of improved COL on CFs immunity for LCC-HVDC, the CFII values of the dual-infeed HVDC system with two different current order limiter control methods are compared: 1) advancing firing angle control with VDCOL; 2) advancing firing angle control with improved COL. Here, the functions of the advancing firing angle control are totally the same in method 1) and method 2). Meanwhile, the VDCOL, adopting the same parameters as the CIGRE HVDC Benchmark model [13], is implemented in method 1), and the
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Fig. 6. Comparison of CFII values in dual-infeed HVDC with control (1) and (2) if the time delay is 2 ms: (a) single-phase fault and (b) three-phase fault. TABLE III PARAMETERS OF THE PCD METHOD
TABLE IV PARAMETERS OF IMPROVED COL
presented improved COL is implemented in method 2). Considering that the purpose of this section is to investigate the impact of improved COL on CF immunity by comparing it with that of VDCOL, the function of advancing firing angle control in both methods is simplified, that is, the firing delay angle is advanced by 5 when the fault is detected. For directly exhibiting the impact of the presented method on CFs immunity of local and remote LCC-HVDC links, only the LCC-HVDC1 in the dual-infeed HVDC is implemented with control method 1 or control method 2, and LCC-HVDC2 just has the VDCOL without advancing firing angle control. Due to limited space, the simulation results of single LCC-HVDC or dual-infeed HVDC with both LCC-HVDC links implemented with presented methods will not be shown in this paper. However, similar conclusions can also be obtained. The parameters of the PCD method and improved COL are shown in Tables III and IV, respectively.
The simulation study is conducted in PSCAD/EMTDC. The zero crossing point from negative to positive phase A voltage is regarded as the reference point, then the fault angle is defined as the angle interval between fault occurring time and the reference point. For dual-infeed HVDC, there is one zero crossing point from negative to positive at 1.9978 s, which is considered as the reference point and the initial fault time. The fault angle varies from 0 to 180 with a 10 step, and the fault lasts 50 ms. In addition, the transmission delay of the dc current order from the inverter to rectifier is also considered here. The CFII curves of LCC-HVDC1 and LCC-HVDC2 with 2-ms transmission delays, under single-phase and three-phaseto-ground faults at the inverter ac busbar of LCC-HVDC1 are obtained as shown in Fig. 6. From Fig. 6(a) with 2-ms time delay, when the single-phaseto-ground fault occurs, the CFII values of LCC-HVDC1 with control (2) increases at the range of (0 , 60 ) and (150 , 180 ) compared with that with control (1). However, it has limited effects on CFs immunity at the fault angle interval of (60 and 150 ). The reasons are as follows. Under the single-phase-toground fault, the commutation voltages of phase A, B, and C are unsymmetrical, which will result in various possibilities of CF for the valves in each bridge. The valves connected at the fault phase are close to or already in the commutation process during the interval of (60 , 150 ); thus, the improved COL could not improve the CFs immunity effectively on these valves in that fault angle area. In addition, it is obvious that the CFs risk of remote LCC-HVDC2 is not reduced by improved COL implemented in LCC-HVDC1, compared with control (1). Under the three-phase-to-ground fault, ac voltage drops symmetrically, which will lead to larger CFs possibility. From Fig. 6(b), the CFII values of LCC-HVDC1 with control (2) are
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V. CONCLUSION
Fig. 7. Commutation process comparison with control (1) and (2) under the single-phase fault.
almost same with that using control (1); thus, the CFs immunity of local LCC-HVDC could not be improved effectively under the three-phase fault condition. However, the improved COL in LCC-HVDC1 can also reduce the risks of CFs for remote LCC-HVDC2. Although the risks of CFs under the three-phase-to-ground fault are not reduced effectively, the proposed method is useful to mitigate the CFs of LCC-HVDC under the single-phase-toground fault, which is the most common fault type in ac systems. It can thus be concluded that the control (2) is generally superior to control (1) in making the LCC less susceptible to CFs. In addition, the improved COL may not mitigate the first CF for some time instants; however, it can potentially reduce the continuous CF risk of LCC-HVDC. The improved COL that is integrated with advancing firing angle control shows the ability to strengthen the CFs immunity, and can make the control system play a better role for CFs mitigation. An example will be given to further demonstrate the improvement of the commutation process by improved COL. A single-phase-to-ground fault, with 84.4 mL inductor grounded, occurs at the inverter ac busbar of LCC-HVDC1 at 1.9978 s, and lasts 50 ms. The simulation results of current order, dc current, commutation voltage, and active power of LCC-HVDC1 with control (1) and (2) are shown in Fig. 7. To further demonstrate the improvement of commutation process by improved COL, the simulation results are obtained based on the condition, that method (1) and method (2) have the same fault detection method (PCD methods) and the same advancing firing angle control. The only difference is that, method (1) adopting classic VDCOL and method (2) adopting proposed improved COL. From the results, the DC current order with control (1) decreases in a linear manner after 2.012 s, however, LCC-HVDC1 has suffered the CF at 2.008 s. With control (2), the DC current order is decreased to 0.75 p.u., roughly 12 ms earlier than that with control (1), after the fault is detected by PCD method. It also can be observed that the DC current decreases and the zero crossing point of the commutation voltage is lagged slightly as compared to the other case. In addition, the power losses with control (2) are limited effectively. Thus, the improved COL integrating with advancing firing angle control improves the commutation process and makes the LCC less susceptible to CFs.
In this paper, a novel power component detection method is presented to recognize the single-phase and three-phase-toground faults, and the corresponding setting principles are also given. Then, considering the slower drop rate of dc current order by VDCOL, an improved COL control strategy is presented to cooperate with the advancing firing angle control to mitigate the CFs for LCC-HVDC. A dual-infeed HVDC system is developed, and the transient performances under single-phase and three-phase-to-ground faults at the inverter ac busbar of one LCC-HVDC link are investigated in PSCAD/EMTDC. From the simulation results, the following conclusions can be obtained. 1) The PCD method, with the voltage and current components as an additional judgment criterion, can achieve faster and more sensitive detection for single-phase and three-phase faults. Compared with the methods taking only voltage or current components for faults recognition, more reliability can be obtained by the PDC method. 2) Under the single-phase fault in dual-infeed HVDC, the improved COL integrated with the advancing firing angle control improves the CFs immunity of local LCC-HVDC; however, it shows a limited effect on remote LCC-HVDC. 3) Under the three-phase fault in dual-infeed HVDC, the improved COL control integrated with the advancing firing angle control cannot reduce the CFs risks of local LCCHVDC effectively; however, it presents the capability to make the remote LCC-HVDC much less susceptible to CFs. 4) Generally, the proposed method increases the commutation margin and improves the CFs immunity for LCC-HVDC. REFERENCES [1] E. Rahimi, A. M. Gole, J. B. Davies, I. T. Fernando, and K. L. Kent, “Commutation failure in single- and multi-infeed HVDC systems,” in Proc. Inst. Elect. Eng., Int. Conf. AC and DC Power Transm., 2006, pp. 182–186. [2] O. B. Nayak, A. M. Gole, D. G. Chapman, and J. B. Davies, “Dynamic performance of static and synchronous compensators at an HVDC inverter bus in a very weak AC system,” IEEE Trans. Power Syst., vol. 9, no. 3, pp. 1350–1358, Aug. 1994. [3] B. R. Andersen and L. Xu, “Hybrid HVDC system for power transmission to island networks,” IEEE Trans. Power Del., vol. 19, no. 4, pp. 1884–1890, Oct. 2004. [4] C.-K. Kim, “Dynamic coordination strategies between HVDC and STATCOM,” in Proc. Transm. Distrib. Conf. Expo.: Asia Pacific, 2009, pp. 1–9. [5] C. Guo, Y. Zhang, A. M. Gole, and C. Zhao, “Analysis of dual-infeed HVDC with LCC-HVDC and VSC-HVDC,” IEEE Trans. Power Del., vol. 27, no. 3, pp. 1529–1537, Jul. 2012. [6] C. V. Thio, J. B. Davies, and K. L. Kent, “Commutation failures in HVDC transmission systems,” IEEE Trans. Power Del., vol. 11, no. 2, pp. 946–953, Apr. 1996. [7] C. Guo, W. Liu, and C. Zhao, “Research on the control method for voltage-current source hybrid-HVDC system,” SCIENCE CHINA Tech. Sci., vol. 56, no. 11, pp. 2771–2777, 2013. [8] A. Hansen and H. Havemann, “Decreasing the commutation failure frequency in HVDC transmission systems,” IEEE Trans. Power Del., vol. 15, no. 3, pp. 1022–1026, Jul. 2000. [9] Y. Z. Sun, L. Peng, F. Ma, G. J. Li, and P. F. Lv, “Design a fuzzy controller to minimize the effect of HVDC commutation failure on power system,” IEEE Trans. Power Syst., vol. 23, no. 1, pp. 100–107, Feb. 2008.
GUO et al.: POWER COMPONENT FAULT DETECTION METHOD AND IMPROVED CURRENT ORDER LIMITER CONTROL
[10] J. Bauman and M. Kazerani, “Commutation failure reduction in HVDC systems using adaptive fuzzy logic controller,” IEEE Trans. Power Syst., vol. 22, no. 4, pp. 1995–2002, Nov. 2007. [11] L. Zhang and L. Dofnas, “A novel method to mitigate commutation failures in HVDC systems,” in Proc. Int. Conf. Power Syst. Technol., 2002, pp. 51–56. [12] Z. Wei, Y. Yuan, X. Lei, H. Wang, G. Sun, and Y. Sun, “Direct-current predictive control strategy for inhibiting commutation failure in HVDC converter,” IEEE Trans. Power Syst., vol. 29, no. 5, pp. 2409–2417, Sep. 2014. [13] M. Szechtman, T. Wess, and C. V. Thio, “A benchmark model for HVDC system studies,” in Proc. Int. Conf. AC and DC Power Transm., 1991, pp. 374–378. [14] P. Kundur, Power System Stability and Control (Authorized English Language Reprint Edition). Beijing, China: Electric Power Press, 2001.
Chunyi Guo (S’09–M’14) received the B.S. and Ph.D. degrees in power system and its automation from North China Electric Power University (NCEPU), Beijing, China, in 2007 and 2012, respectively. Currently, he is a Lecturer of Power Grid with New Energy Institute, NCEPU. His research interests include LCC-HVDC, VSC-HVDC, and ac/dc interaction analysis.
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Yuchao Liu received the B.S. degree in power systems and its automation from North China Electric Power University (NCEPU), Beijing, China, in 2011, where he is currently pursuing the M.Sc. degree in power system and automation. His research field includes HVDC and flexible ac transmission systems.
Chengyong Zhao (M’05) received the B.S., M.S., and Ph.D. degrees in power system and its automation from North China Electric Power University (NCEPU), Beijing, China, in 1988, 1993, and 2001, respectively. Currently, he is Deputy Director of Power Grid with New Energy Institute, NCEPU. His research interests include HVDC and flexible ac transmission systems.
Xiaoguang Wei received the B.Eng. and M.Eng. degrees in power system and its automation from North China Electric Power University (NCEPU), Beijing, China, in 1999 and 2003, respectively, and the Ph.D. degree in electrical engineering from China Electric Power Research Institute (CEPRI), Beijing, in 2007. Currently, he is Vice President of the Engineering of DC Transmission Technology Institute in State Grid Smart Grid Research Institute, mainly engaged in dc transmission technology.
Weihua Xu received the B.Eng., M.Eng., and Ph.D. degrees in power system and its automation from North China Electric Power University (NCEPU), Beijing, China, in 2004, 2006, and 2010, respectively. In 2012, she joined the State Grid Smart Grid Research Institute, Beijing, China. Her research interests are electrical design and protection of the UHVDC converter valve.
