COMPARISON OF GRID CONNECT MULTI-LEVEL INVERTER

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1 ISSN: (Print) ISSN: (Online) COMPARISON OF GRID CONNECT MULTI-LEVEL INVERTER MILAD TEYMOORIYAN a1 AND MAHDI SALIMI b ab Department of Engineering, Ardabil Branch, Islamic Azad University, Ardabil, Iran ABSTRACT In this paper, multilevel inverters structures are compared. These converters consist of series H-bridge inverter, diode clamping and floating capacitors. The study also investigates the advantages and disadvantages of the different topologies. Finally, the structures which can be used in combination with multi-level inverter connected to the grid have been developed. KEYWORDS: Multi-Level Inverter In recent years, new industrial applications for medium and high voltage motors (which may require voltages in megawatts ranges) applied these inverters which can be used as an alternative to the power of a multilevel converter for high and medium renewable energy sources. The use of multilevel converters has been started since 1975 [1], which is in fact the development of the two-level converters. Purpose of the use of multilevel converters, access to a high power is the key to a series of semiconductor strength and low DC voltage sources for energy conversion based on elements such as capacitors, batteries and renewable energy sources is implemented. Using the appropriate switching and considering several sources of input DC converters, high voltage can be obtained in a multilevel converter output. Multilevel converters have advantages and disadvantages compared to two level converters considering switching frequency and Pulse Width Modulation (PWM) can include. 1- Quality of the AC output waveform: a multilevel converter cannot only produce a voltage output with extremely low distortion, also capable of decreased stress dv /dt. So the problem of electromagnetic interference (EMI) can be reduced. 2 - Less Common Mode voltage (CM): less CM voltage multilevel converters and therefore less stress on the motor bearings as well as semiconductor components connected to a multi-level inverter will be reduced. [2] 3 - The input source: the use of multilevel converters can already having low distortion input sources, problems related to power quality in distribution systems to overcome. 4 - Switching frequency: multilevel converters can be both primary and high switching frequency to be used. Lower switching frequency usually means higher efficiency as well. The disadvantages of multilevel converters can also be summarized as follows: 1 - To be expensive due to the high number of switching elements (which cannot be economically affordable.) 2 - Design complexity due to the lack of sufficient knowledge (creates problems) 3 - Different techniques for controlling converters, multilevel provided. Example can be pulse width modulation sine, eliminating the harmonic selective modulation vector space mentioned. Most important applications of inverters multilevel can to drive motors, medium voltage, transmission systems AC flexible and renewable energy sources are connected to the grid [4, 3]. In this section, the advantages and disadvantages of multilevel converters, kind of actives switch usage, how to charge and discharge the closing of diodes and capacitors of the converter structure and especially for the inverter connected to the grid will be reviewed. PREPARE YOUR PAPER BEFORE STYLING Transformers series H: Structure of the converter in Figure 1 is shown. Figure 1: Structure of a single-phase H-bridge converter 1 Corresponding author

2 H-bridge converters successively by each of the three levels voltage [-Vdc 0 Vdc+ ] won with a separate DC sources in Figure 1 is shown. Using multilevel converters are can the state inverter, rectification, charging and braking could be. How to remove harmonics of the fifth, seventh, eleventh and thirteenth on a suitable switching lowfrequency figure (2) is shown in [5]. Figure 2: Eleven level H-bridge converte with five separate DC source disadvantages of the H-bridge multilevel inverter are as follows: Advantages: 1 - number of output voltage levels more than twice the number of DC input sources (M = 2m +1) in this regard: M: number of output levels m: number of H-bridge used in each phase 2 - There is packet-like modules. 3 - Design of control system is very simple. Disadvantages: 1- separate DC sources required for each H-bridge Diode clamped multilevel inverter in [6]. Structure of such a converter in Figure 4 is given Figure 4: Structure of three-phase inverter based on diode-clamped In Figure 3 the application of multi-level inverter for electric vehicles is presented. Figure 3: Multi-level three-phase inverter based on sequential H-bridge to drive the electric motor with the batteries located in the DC Converter Inverter shown in Figure (4) instead of the threelevel output voltage level output for multiple uses. For example, in Figure 4, six-level inverter output voltage is used and the principles in Table 1 and Figure (5) are given. The circuit shown in Figure (3) is able to drive the electric motor and batteries located in the dynamic braking of DC side of the inverter used. Advantages and

3 Table 1: Diode clamped inverter and switches voltage level corresponding to six different Figure 5: The voltage waveform of the inverter linelevel diode clamped six Advantages and disadvantages of such a converter is discussed in [8.7]. Advantages: 1. All phases of the DC capacitors are identical, so the fewer the number of capacitors required. 2. Ability to charge the capacitors of the group is allowed. 3. The switching frequency of the main component, the converter efficiency is high. Disadvantages: 1. Ability to pass the real power of the system is very difficult because the capacitor charging or discharging Add to Medieval tend voltage may be unbalanced. 2. The number of clamping diodes required levels is related to the square of the number of diodes can increase exponentially. Floating capacitor based multilevel inverter [9]: Figure 6: Structure of three-phase inverter six levels based on the floating capacitor Figure (6) shows, instead of clamping diodes are used in a manner different from that usedcapacitors to increase voltage output waveform and There is no resemblance between the diode and clamps'.

4 Table 2: Usage-based inverter is shown floating capacitors [11, 10]. The advantages and disadvantages of using a converter based on the floating capacitors can be summarized as follows: Figure 7: P2 generalized multilevel topology for a multilevel inverter Advantages: 1. Adding capacitors to balance the voltage levels are available. 2. Active and reactive power flow can be maintained easily. Disadvantages: 1. Complex control voltage due to variations in their numbers. 2. Before charging capacitors, circuit startup are associated with problems. 3. The large number of capacitors increases the complexity of life, cost, and size. Combination of structures 1 - Floating capacitance diode clamped multilevel inverter can be combined with a new structure obtained in the form (7) is shown. The multilevel topology can balance each voltage level to produce. Two-level converters can also be achieved with this topology [12] 2 - Hybrid multilevel converters: To reduce the number of independent sources in a DC high voltage applications can be structured as shown in Figure (8) can be used [13]. The main drawback to this method is the complexity of its design.

5 Figure 8: A hybrid multilevel inverter using three-level diode-clamped H-bridge structure is used as the primary cells [15.14]. inverters is in inverter mode and another is in rectification work. Such an arrangement is well suited to drive high power electric motors. Figure 10: Structure of the diode clamped converter with six consecutive 3- Multilevel inverter switching software: a multilevel converter in this case in order to avoid switching losses and increase efficiency are used. Figure 9: Diode clamped inverter with soft switching in CONCLUSION In this paper, a multilevel inverter consists of 1 - H -bridge inverter based multilevel successive, 2 - H -bridge inverter based on multi-level squence of charge and discharge capabilities by batteries located in the DC inverter, 3 - Phase six diode clamped inverter with, 4 - three-phase inverter based on six levels floating capacitor,5 - P2 generalized topology multi-level multilevel inverter to convert the power output of, 6 - Hybrid multilevel inverter, 7 - Diode clamped inverter with soft switching in, 8 - six- level inverter converts the comparison. These comparisons include the advantages and disadvantages of each of them be. In Table (3 ), the comparison of different multilevel inverters in presented. 4- Converters with diode clamped back to back: Use the same inverter converters with diode clamped in the form (10) is shown [17.16]. In this structure, one of the Table 3: Comparison of multilevel inverter Inverters Advantages Disadvantages

6 Consecutive H-bridge inverter Diode clamped multilevel inverter with Floating capacitor multilevel inverter based 1-number of output voltage levels more than two times the number of sources 2 - Ability Classification System Modules are like. 3 - Design of control system is very simple. Using the same DC 1 - Keying phase capacitors That are why many smaller capacitors are required 2 - the possibility of charging the capacitor as a whole is possible. 3 - The switching frequency of the main component, the converter efficiency is high. 1- Add capacitor voltage balancing is available. 2 -Active and reactive power flow can be controlled 3 - Using a large number of input capacitors enables the elimination of the long output inverter can provide. Needed to separate H-bridge DC Sources 1- Ability to pass the real power of the system is very difficult because they tend to charge and discharge the capacitors tend to add. 2 - The number of clamping diodes lining increases exponentially with the square of the number of connections they are needed. 1- Complete control voltage due to the multiplicity of their 2 - Before charging capacitors, circuit startup problems associated. 3 - Number of capacitors complicated, more expensive and has more volume. REFERENCES R. H. Baker and L. H. Bannister, Electric Power Converter, U.S.Patent , Feb E. Cengelci, S. U. Sulistijo, B. O. Woom, P. Enjeti, R. Teodorescu, and F. Blaabjerg, A New Medium Voltage PWM Inverter Topology for Adjustable Speed Drives, in Conf. Rec. IEEE-IAS Annu. Meeting, St. Louis, MO, Oct. 1998, pp L. M. Tolbert, F. Z. Peng, and T. G. Habetler, A Multilevel Converter-based Universal Power Conditioner, IEEE Transactions on Industry Applications, vol. 36, no. 2, Mar./Apr. 2000, pp L. M. Tolbert, F. Z. Peng, and T. G. Habetler, Multilevel Inverters for Electric Vehicle Applications, IEEE Workshop on Power Electronics in Transportation, Oct , Dearborn, Michigan, pp R. W. Menzies and Y. Zhuang, Advanced Static Compensation Using a Multilevel GTO ThyristorInverter, IEEE Transactions on Power Delivery, vol. 10, no. 2, Apr. 1995, pp A. Nabae, I. Takahashi, and H. Akagi, A New Neutralpoint Clamped PWM Inverter, IEEE Transactions on Industry Applications, vol. IA- 17, Sept./Oct. 1981, pp C. Hochgraf, R. Lasseter, D. Divan, and T. A. Lipo, Comparison of Multilevel Inverters for Static VarCompensation, Conference Record IEEE Industry Applications Society 29th Annual Meeting, 1994, pp J. S. Lai and F. Z. Peng, Multilevel Converters A New Breed of Power Converters, IEEE Transactions on Industry Applications, vol. 32, no. 3, May 1996, pp T. A. Meynard and H. Foch, Multi-Level Conversion: High Voltage Choppers and Voltage-Source Inverters, IEEE Power Electronics Specialists Conference, 1992, pp J. S. Lai and F. Z. Peng, Multilevel Converters A New Breed of Power Converters, IEEE Transactions on Industry Applications,vol. 32, May/June 1996, pp L. M. Tolbert, F. Z. Peng, and T. Habetler, Multilevel Converters for Large Electric drives, IEEE Transactions on Industry Applications, vol. 35, Jan./Feb. 1999, pp F. Z. Peng, A Generalized Multilevel Converter Topology with Self Voltage Balancing, IEEE Transactions on Industry Applications, vol. 37, Mar./Apr. 2001, pp W. A. Hill and C. D. Harbourt, Performance of Medium Voltage Multilevel Converters, in Conf. Rec. IEEE-IAS Annu. Meeting, Oct. 1999, Phoenix, AZ, pp

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