Inter national J our nal of P o wer Electr onics and Dri v e System (IJPEDS) V ol. 11, No. 4, December 2020, pp. 1883 1889 ISSN: 2088-8694, DOI: 10.11591/ijpeds.v11.i4.pp1883-1889 r 1883 A high-perf ormance multile v el in v erter with r educed po wer electr onic de vices Amer Chlaihawi, Adnan Sab bar, Hur J edi Department of Electrical Engineering, Uni v ersity of K uf a, Iraq Article Inf o Article history: Recei v ed Feb 20, 2020 Re vised Apr 26, 2020 Accepted May 19, 2020 K eyw ords: High-performance operation Multile v el in v erter (MLI) Nearest le v el modulation (NLM) ABSTRA CT This paper introduces a ne w topology of multile v el in v erter , which is able to operate at high performance. This proposed circuit achie v es requirements of reduced number of switches, g ate-dri v e circuits, and high design fle xibility . In most cases fifteen-le v el in v erters need at least twelv e switches. The proposed topology has only ten switches. The in v erter has a quasi-sine output v oltage, which is formed by le v el generator and polarity changer to produce the desired v oltage and current w a v eforms. The detailed operation of the proposed in v erter is e xpl ained. The theoretic al analysis and design procedure are gi v en. Simulation results are presented to confirm the analytical ap- proach of the pr oposed circuit. A 15-le v el and 31-le v el multile v el in v erters were de- signed and tested at 50 Hz. This is an open access article under the CC BY -SA license . Corresponding A uthor: Adnan Sabbar , Department of Electrical Engineering, Uni v ersity of K uf a, Najaf, Iraq. Email: adnan.sabbar@uokuf a.edu.iq 1. INTR ODUCTION W ith the rapid de v elopment of po wer electronics, the demand of po wer con v erters are high perfor - mance, lo w cost and high po wer quality applications [1–3]. Reducing the number of switches in po wer elec- tronics can impro v e the po wer density and leads to lo w v oltage stress on switches [4–7]. Multile v el con v erters can att ain both fundamental switching frequenc y and high switching frequenc y PWM [8–10]. Therefore, mul- tile v el in v erters with separate DC sources are suited for operation at lo w frequenc y to achie v e lo w switching losses and high ef ficienc y [11–13]. In v erters in such application handle high v oltage and e xtensi v e po wer . Thus, high-le v el in v erters, which are compos ed of switching po wer de vices inte grated g ate bipolar transistors (IG- BTs), are suitable t o achie v e high v oltage applications [14, 15]. Most con v entional multile v el in v erters, such as Flying Capacitor (FC), Neutral Point Clamped (NPC), and Cascaded H-Bridge (C HB) suf fer from high-v oltage stress on switch, high Electro Magnetic Interference (EMI) and poor po wer quality output [16–18]. In order to solv e these issues, a ne w topology of multile v el in v erter is presented. In last fe w decades, se v eral authors ha v e been increasingly focused on multile v el in v erter topologies with reduction in numbers of po wer switches [19–23]. T opology [24] is combined of IGBT and diode causing reduction in ef ficienc y . In addition, the losses and cost will be increased and its industrial applications will be restricted. In [25] sub-multile v el con v erter blocks are connected in series. This circuit consists of capacitors and four bi-directional switches are utilized in each unit. Thus, the installation area i s increased in the proposed topology . Most of the multile v el in v erters suf fer from high v oltage stresses at the po wer switches and require dif ferent v oltage rating of the po wer switches. In addition, switching frequenc y leads to a decrease in ef ficienc y J ournal homepage: http://ijpeds.iaescor e .com Evaluation Warning : The document was created with Spire.PDF for Python.
1884 r ISSN: 2088-8694 due to switching losses. Therefore, the proposed topology is attracti v e for high-performance applications. This w ork proposes a high po wer quality multile v el in v erter with reduced in numbers of po wer semi- conductor de vices. The proposed topology can attain a lar ge number of le v els with asymmetric DC v oltage sources. This topology is based on the con v entional in v erter that utilizes le v el generation and polarity change. The ne w circuit can be utilized for 15-le v el and 31-le v el in v erter . T o implement a 15-le v el in v erter , ten IGBT switches and three dc v oltage sources are selected. The multile v el in v erter generates staircase v oltage w a v eform with decreased electromagnetic compatibility (EMC) issues and lo w distortion. The ne w topology also utilizes lo w number of po wer switches and includes a lo w-design comple xity . The described topology also sho ws in details the analysis of the steady-state v oltage w a v eforms. In order to determine an appropri ate characteristics of the multi le v el in v erter , a design procedure has been applied. The proposed circuit w as si mulated and tested at a frequenc y of 50 Hz. A c on t rol unit of signals are used to generate fix ed v alues of operating frequenc y and duty ratio. Collecti v ely , these fe atures mak e the ne w multil e v el in v erter adv antageous in applications , such as A C dri v es and F A CTS de vices. 2. AN AL YSIS OF THE PR OPOSED MUL TILEVEL INVER TER T OPOLOGY Figure 1 sho ws the proposed multile v el in v erter circuit. The proposed topology consist of le v el gen- erate and polarity change. The le v el generation has po wer switch P i and po wer switch S i , which is connected in series with the DC v ol tage source V i . The circuit of polarity change is comprised H-Bridge po wer switches H S i and connected in parallel with the load. In this study , IGBT transis tors, which ha v e high switching perfor - mance, are used in the proposed topology . W e focus on identifying the characteristics of the proposed in v erter to pro vide a fle xible output v oltage w a v eform across the load of the circuit with minimum number of switches.     Figure 1. Proposed multile v el in v erter circuit The ne w topology can produce fifteen-le v el output during asymmetric condition. The operating modes during asymmetric operation of the circuit to obtain alternating output v oltage across the load is sho wn in Figure 2. The proposed topology requires six switches and three DC v oltage sources to generate positi v e-le v els steps output v oltage at the load as sho wn in the left part of the in v erter . A polarity changer , which is comprised of four switches, is added to generate the ne g ati v e-le v els steps output v oltage at the load. The switches H S i are utilized to re v erse the polarity of the output v oltage of the in v erter . The analysis of the proposed circuit is based on the the O N -state and the O FF -state of the switches P i and S i , respecti v ely . The switches H S 1 and H S 4 are O N during the positi v e c ycle of the operation, while the switches H S 2 and H S 4 are O FF during the ne g ati v e c ycle of the operation. Int J Po w Elec & Dri Syst, V ol. 11, No. 4, December 2020 : 1883 1889 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 r 1885 Figure 2. Operation mode of switches. Figure 3 sho ws the illustrating operation of idealized steps of the circuit o v er a period. As can be seen, each step for output v oltage is double of the v oltage source V i . The switches P i and S i of the in v erter can be deri v ed according to the control unit circuit to generate pulse width modulator w a v eforms as sho wn in Figure 4. Figure 3. Le v el modulation technique Figure 4. Control unit of signals for 15-le v el switches T o establish the design equations, the circuit beha vior is analyzed in each interv al. It is considered V i as a reference v oltage in the proposed multile v el in v erter . The number of DC v oltage sources N V base on the number of unit cell m in the in v erter N = 2 m ; (1) where, m = 0 ; 1 ; 2 ; 3 :::i . The steps of output v oltage D steps can be found as D steps = 2 i +2 1 : (2) The maximum output v oltage v O is the sum of DC v oltage sources N v O = D steps 1 2 V i : (3) The po wer switches of the proposed topology can be switched at an y duty c ycle D . It can be determined based on the specifications of the multile v el in v erter . A high-performance multile vel in verter with r educed power electr onic de vices (Amer Chlaihawi) Evaluation Warning : The document was created with Spire.PDF for Python.
1886 r ISSN: 2088-8694 3. DESIGN PR OCEDURE A design procedure for the ne w multile v el in v erter is presented to supply a resisti v e load at operating frequenc y f s = 50 Hz. In the design procedure, the follo wing design parameters V i , v O , and D are determined. The reference DC v oltage source V i for 15-le v el and 31-le v el were chosen to be 45 V and 20 V , respecti v ely . Furthermore, the duty c ycle of po wer switches is 50%. The reference DC v oltage V i can be selected basing on the application of the in v erter . In the proposed circuit, the designer can easily adjust the v alue of duty c ycle to achie v e the re qu i red dri v en v oltage w a v eform of the p o we r switches. F or 15-le v el output and step v oltage 45 V , the peak-to-peak output v oltage of the multile v el in v erter is v aried from +312 to -312. F or the 31-le v el in v erter , the reference DC v oltage V i = 20 V is applied at the proposed circuit, the peak v alue of v oltage stress is 312 V at duty c ycle D = 50%. The peak v alue of the v oltage stress depends on the total DC source v oltage on the po wer switch. The v alue of v GE v oltage based on the characteristics of the po wer switch IGBT in the in v erter . Therefore, it is important to select a proper dri ving v oltage rating for the po wer switch. In this w ork, the v oltage v GE rating of the po wer switch, which is utilized in the g ate dri v er , is 20 V . The tr ansistor B UP306D w as utilized as a IGBT po wer switch in circuit. The load of the proposed in v erter is chosen to be a resisti v e load R L = 50 . The major dif ferences between the proposed topology and the popular multile v el in v erters ar e the number of po wer switches and the type of switching. Thus, most multile v el in v erter circuits operate at least twelv e po wer switches. T o operate fifteen-le v el in v erter , the proposed multile v el in v erter has six switches in the le v el generation and four switches in the H-bridge. Furthermore, the switching beha vior of IGBT transistors in the proposed multile v el in v erter can achie v e high v oltage applications. Therefore, the performance of the in v erter can increase the ef ficienc y of the in v erter . These features sho w the the adv antage of the ne w circuit. The specifications and parameters of the circuit are gi v en in T able 1. T able 1. List of parameters for multile v el in v erter at f s = 50 Hz Components V alue B UP306D V C E = 1200 V , V GE = 20 V , I C = 23 A C iss = 1300 pF , C oss = 100 pF , C r ss = 50 pF R 50 V i 45 V , 20 V 4. SIMULA TION RESUL TS Based on the design methodology and the circuit operation, the proposed multile v el in v erter has been v erified through MatLab simulation. The performance of the proposed topology during the asymmetric oper - ation is analyzed. A 50 Hz PWM signal is used to supply the po wer switches, and the v alue of duty c ycle is D = 0.5. A B UP 306D IGBT po wer switch with anti parallel diode (1200 V , 23 A) from Siemens w as used as the po wer transist or in the multile v el in v erter circuit. In order to mak e the circuit operates in high performance, this po wer switch is optimized for lo w switching losses and high-speed operating. The proposed topology is simulated for 15-le v el in v erter and 31-le v el in v erter , respecti v ely . 4.1. 15-le v el multile v el in v erter T o generate appropriate switching Pulse W idth Modulation schemes for the po wer switches, the circuit in Figure 4 is used. The fundamental frequenc y is utilized to generate the s witching pulses in the circuit. According to the switching states, the pulses are generated at each step to dri v e the po wer switches as sho wn in Figure 5. If the pulses form accurately , the ef ficienc y and harmonic distortion can be controlled ef fecti v ely in the proposed multile v el in v erter . The switches of H-bridge are operated in a complementary mode to produce the positi v e and the ne g ati v e le v els steps output v oltage at the load. The in v erter pro vides the A C signal with a peak magnitude 312 V to the load, when the dc v oltage source is 45 V . In order to observ e the step v oltage w a v eform at the output resistor , the zoomed w a v eform of the output v oltage for the multile v el in v erter is sho wn in Figure 6. It can be seen that the step size of the w a v eform is 45 V . The step le v el of the in v erter w as captured in Figure 7. It is clear that the output v oltage is close to sine w a v eform. The presented approach pro v es that the ne w in v erter pro vides lo w-v oltage stress and small-v alued components. Int J Po w Elec & Dri Syst, V ol. 11, No. 4, December 2020 : 1883 1889 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 r 1887 Figure 5. Simulated 15-le v el switching pulse w a v eforms of multile v el in v erter Figure 6. Simulated of 15-le v el zoomed output v oltage w a v eform Figure 7. Simulated of 15-le v el multile v el in v erter w a v eform 4.2. 31-le v el multile v el in v erter The proposed topology can be utilized for 31-le v el to generate A C w a v eform close to sine signal. The po wer switches of 31-le v el circuit are deri v ed by the control circuit to form switching pulses as sho wn in Figure 8. The output v oltage w a v eform in Figure 9 sho ws the operation of 31-le v el of the proposed topology . It is clearly sho ws that the operation of the circuit is obtained by the le v el generation and change polarity circuit to supply the A C signal to t he load. The maximum v alue of the v oltage stress w as measured as 312 V for the input v oltage V = 20 V . The peak-to-peak output v oltage of the multi le v el in v erter across the load is v aried from +185 to -185. It can be noticed that the output v oltage is close to sine w a v eform. A high-performance multile vel in verter with r educed power electr onic de vices (Amer Chlaihawi) Evaluation Warning : The document was created with Spire.PDF for Python.
1888 r ISSN: 2088-8694 Figure 8. Simulated 31-le v el switching pulse w a v eforms of multile v el in v erter Figure 9. Simulated 31-le v el multile v el in v erter w a v eform. 5. CONCLUSION A ne w switched-mode multile v el in v erter , which is deri v ed from con v entional multile v el in v erter , has been introduced. This topology operates at constant duty c ycle and frequenc y . The ne w topology can be designed for 15-le v el and 31-le v el in v erter . An H-bridge is added in the proposed topology to generate ne g ati v e v oltage le v els. It has a lo w number of po wer switches, lo w switch v oltage stress, lo w DC v oltage sources, and fle xible design. The ne w circuit is designed to s up pl y A C signal to the load e v en when lo w-input v oltage of the in v erter is a v ailable. Based on abo v e analysis, the prototype with 50 Hz w as designed and simulated. The simulation testing results demonstrate a good agreement between the simulations and the calculations. The proposed circuit can be used in applications that demand high performance, such as F A CTS controllers and adjustable motor dri v es. REFERENCES [1] G. Ce glia, et al. , A Ne w Simplified Multile v el In v erter T opology for DC–A C Con v ersion, IEEE T r ans- actions on P ower Electr onics , v ol. 21, no. 5, pp. 1311-1319, Sep. 2006. [2] A. Chlaiha wi, et al. , “No v el Screen Printed and Fle xible Lo w Frequenc y Magneto-Electric Ener gy Har - v ester , IEEE Sensor s , 2016, pp. 1-3. Int J Po w Elec & Dri Syst, V ol. 11, No. 4, December 2020 : 1883 1889 Evaluation Warning : The document was created with Spire.PDF for Python.
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A high-performance multile vel in verter with r educed power electr onic de vices (Amer Chlaihawi) Evaluation Warning : The document was created with Spire.PDF for Python.