Z-Source Based Multi Level Inverter

Z-Source Based Multi Level Inverter

Z-Source Based Multi Level Inverter

Anand kumar T, Kannan.C, Ponmanikandan P

Assistant Professor Assistant Professor

Dr.Mahalingam College of Engineering & Technology

Vol. 2 Issue 5, May – 2013

This paper presents a novel single Z-source based seven level multilevel inverter. In this topology single Z-source impedance network is used to boost up the output voltage using shoot through state control. A new PWM technique is implemented by using three reference signals and a triangular carrier signal which are used to generate the PWM signals for inverter switches, and the shoot through state for Z-network is achieved by inserting DC reference signal. The advantage of proposed topology makes reduction in number of switches, and this new configuration is suitable for applications working at lower and medium power levels. The performance of proposed topology is validated using MATLAB/SIMULINK software.

Index Terms Z-source inverter, multilevel inverter, renewable energy resource.

I

I

1. N RECENT years, due to energy crisis, renewable energy resource, such as wind turbine, photovoltaic (PV) cell, and fuel cell are becoming more and more popular in industrial and residential applications [1]. Photo-Voltaic (PV) sources are used today in many applications as they have the advantages of being maintenance and pollution free. Solar-electric-energy demand has grown consistently by 20%25% per annum over the past 20 years, which is mainly due to the decreasing costs and prices. This decline has been driven by the following factors: 1) an increasing efficiency of solar cells 2) manufacturing technology improvements

   and 3) economics of scale.

   In the conventional PV array systems, the other converter as a DC-DC boost chopper is utilized to increase output DC voltage of the PV. In the suggested topology, Z-source inverter is employed instead of DC- DC boost chopper. The Z-source inverter utilizes Z impedance network between the DC source and inverter circuitry to achieve boost operation [2]. The voltage boost is achieved by providing a shoot-through state when both switches in the same phase leg are on which is not possible with traditional inverter topology. The Z- Source inverters in the comparing of traditional inverters are lower costs, reliable, lower complexity and higher efficiency [3-4].

   Various topologies for multilevel inverters have been proposed over the years. Common ones are diode- clamped [5][8], cascaded H-bridge [9-10], and modified H-bridge multilevel [11][15].

   TABLE I

   COMPARITION OF MULTILEVEL INVERTER

   Multilevel Inverter type	H bridge Auxiliary switch	Diode Clamped	Capacitor Clamped	Asymmetric Cascade
   Main switch	4	36	36	36
   Required blocking voltage	Vs/2	Vs/7	Vs/7	Vs/7
   Anti parallel diodes	8	36	36	36
   Auxiliary switches	2	36	–	–
   Required blocking voltage	Vs/3	–	–	–
   Auxiliary diodes	4	–	–	–
   Switches total	6	36	36	36
   Diodes total	12	72	36	36
   Capacitors	3	7	17	9

   Multilevel inverter, which used to convert dc power obtained from PV modules into ac power. Multilevel inverters are promising; they have nearly sinusoidal output-voltage waveforms, output current with better [16-17].

   Fig.1. Proposed single Z-source based multilevel inverter

   They offer improved output waveforms, smaller filter size, lower EMI and lower total harmonic distortion (THD). This paper recounts the development of a novel modified H-bridge single-phase multilevel inverter that

   has two diode embedded bidirectional switches and a novel pulse width modulated (PWM) technique.

   It is assumed that average voltage of inductor Vol. 2 Issue 5, May – 2013

   is zero so

   is zero so

   relation between capacitor and output voltage is found as:

2. V c = V i n

   T n s

   T n s – Ts h

   ( 7 )

   1. Z-source network

      Fig. 2(a) shows the suggested basic unit for a proposed Z-source topology. This consists of a DC

      Where Tsh is the total shoot-through state period and Tns is the total non shoot-through state period during all period of switching. Substituting (8) in to (7) during non shoot through state Vin is obtained as

      voltage source, Z impedance with one switch S7 and

      V = V d c

      ( 8 )

      Diode DS. It can operate in two modes: non shoot- through and shoot-through state. In the shoot-through

      i n T

      s h

      s h

      1 – 2

      T

      1

      state, switch S7 is on and diode DS off output voltage of

      B =

      1 – 2 T s h

      ( 9 )

      z-network is zero. The shoot-through pulse is generated by comparing a dc reference line with the triangular carrier wave.

      1. Shoot-through state:

         The equivalent circuit of shoot-trough state is shown in Fig. 2(b). With the analysis of circuits 2(b) it can be expressed as:

         T

         Where T is period of switching and B is boost factor and it is clear that B 1.

         TABLE II

         SWITCHES STATES AND Vo VALUE

         State	Output Voltage(V0)	Switches
         1	Vin(Non Shoot-through)	S7 OFF, DS ON
         2	0(Shoot-through)	S7 ON, DS OFF

         V L = V c

         ( 1 )

   2. Multilevel inverter topology

   V i n

   = 0 ( 2 )

   1. Non Shoot-through state:

   The equivalent circuit in non shoot-through state is shown in Fig. 2(c). Inductors voltage and output of LC network can be calculated as:

   The proposed single-phase seven-level inverter was developed from the five-level inverter in [11][12]. It consist of a single-phase conventional H-bridge inverter, two bidirectional switches, and a capacitor

   voltage divider formed by C1, C2, and C3, as shown in

   V L = V d c

   – V c

   ( 3 )

   (Fig. 1). The modified H-bridge topology is significantly

   Vin

   = Vc – VL

   ( 4 )

   advantageous over other topologies, i.e., less power

   V i n

   = 2 V c

   – V d c

   ( 5 )

   switch, power diodes, and less capacitors or inverters of the same number of levels. Photovoltaic (PV) arrays were connected to the inverter via a single z-source converter. Proper switching of the inverter can produce seven output-voltage levels (Vdc, 2Vdc/3, Vdc/3, 0, Vdc,

   2Vdc/3, Vdc/3) from the dc supply voltage.

   TABLEIII

   SWITCHING STATES OF PROPOSED INVERTER

   (a)

   (b)

   (c)

   Fig.2 Circuit diagram of (a) single phase proposed basic unit, (b) basic unit in shoot through state, (c) basic unit in non shoot through state.

   S1

   V0	S2	S3	S4	S5	S6
   Vdc	On	Off	Off	On	Off	Off
   2Vdc/3	Off	Off	Off	On	On	Off
   Vdc/3	Off	Off	Off	On	Off	On
   0	Off	Off	On	On	Off	Off
   0*	On	On	Off	Off	Off	Off
   -Vdc/3	Off	On	Off	Off	On	Off
   – 2Vdc/3	Off	On	Off	Off	Off	On
   -Vdc	Off	On	On	Off	Off	Off

3. PWM switching signals are generated by a novel PWM modulation technique. Three reference signals (Vref1, Vref2, and Vref3) were compared with a carrier signal (Vcarrier).The reference signals had the same frequency and amplitude and were in phase with an offset value that was equivalent to the amplitude of the carrier

   signal. The reference signals were each compared with the carrier signal. If Vref1 had exceeded the peak amplitude of Vcarrier, Vref2 was compared with Vcarrier until it had exceeded the peak amplitude of Vcarrier. Then, onward, Vref3 would take charge and would be compared with Vcarrier until it reached zero. Once Vref3 had reached zero, Vref2 would be compared until it reached zero. Then, onward, Vref1 would be compared with Vcarrier. The shoot-through pulse for Z-source network is generated by comparing dc reference line with the carrier signal. Shoot-through time varies depending on the magnitude level of dc reference line as compared with Vcarrier.

   Fig.5 (a) PWM signal for S1

   Fig.5 (b) PWM signal for S2

   Vol. 2 Issue 5, May – 2013

   Fig.3 Proposed PWM Technique

4. The PWM switching patterns were generated by comparing three reference signals (Vref1, Vref2, and Vref3) against a triangular carrier signal (see Fig. 4). One leg of the inverter operated at a high switching rate that was equivalent to the frequency of the carrier signal, while the other leg operated at the rate of the fundamental frequency (i.e., 50 Hz). Switches S5 and S6 also operated at the rate of the carrier signal. The shoot-through pulse is shown in fig.5 (g).

   TABLE IV

   Z-Source Network

   Parameters	Value
   L1,L2	1mH
   C1,C2	2600uH

   Simulation result of 7- Level Multilevel Inverter at switching frequency 3 kHz, 230V, 4A, 720W were shown in fig (6 & 7). The seven-level inverter produces lowest THD value (0.42%) as compared with five and three-level inverter with filter shown in fig (9).

   Fig .4 Proposed PWM switching pattern

   Fig.5 (c) PWM signal for S3

   Fig.5 (d) PWM signal for S4

   Fig.5 (e) PWM signal for S5

   Fig.5 (f) PWM signal for S6

   Fig.5 (g) Shoot-Through pulse for S7

   Fig.6 Inverter output voltage (Vout)

   Fig.7 Harmonic analysis for output Voltage (without filter)

   Fig.8 Harmonic analysis for output Voltage (with filter)

In this paper the modeling and simulation of novel single Z-source based multilevel inverter have been shown. The PWM switching signals are generated by comparing three reference signals against a triangular carrier signal. The voltage level of the PV panel is improved using Z-source network & multilevel inverter. The proposed multilevel inverter is to reduce both voltage & current THD of the inverter .The proposed topology has minimum number of switches compare than other configuration.

1. B. K. Bose, Energy, environment, and advances in power electronics, IEEE Trans. Power Electron., vol. 15, no. 4, pp. 688701, Jul. 2000.

2. Miaosen Shen, Stefan Hodek, Fang Z.Peng, "Control of the Z-Source Inverter for FCHEV with the battery Connected to the Motor Neutral Point", Power Electronics Specialists Conference, pp. 1485-1490,2007 .

3. Amitava Das, Debasish Lahiri, A.K.Dhakar , Residential Solar Power Systems Using Z-Source Inverter", TENCON, IEEE Regional 10 Conference, 2008.

4. Jin Wang, Fang Z. Peng, Leon M. Tolbert, Donald J. Adams, "Maximum Constant Boost Control of the Z- Source Inverter " , Industry Application Conference, 39 th Annual meeting Conference Record, Vol.1,2004.

5. J. Rodríguez, J. S. Lai, and F. Z. Peng, Multilevel inverters: A survey of topologies, controls, and applications, IEEE Trans. Ind. Electron., vol. 49, no. 4, pp. 724738, Aug. 2002.

6. J. Rodriguez, S. Bernet, B. Wu, J. O. Pontt, and S. Kouro, Multilevel voltage-source-converter topologies for industrial medium-voltage drives, IEEE Trans. Ind. Electron., vol. 54, no. 6, pp. 29302945,Dec. 2007.

7. M. M. Renge and H. M. Suryawanshi, Five-level diode clamped inverter to eliminate common mode voltage and reduce dv/dt in medium voltage rating induction motor drives, IEEE Trans. Power Electron., vol. 23, no. 4, pp. 15981160, Jul. 2008.

8. E. Ozdemir, S. Ozdemir, and L. M. Tolbert, Fundamental- frequency modulated six-level diode-clamped multilevel inverter for three-phase stand-alone photovoltaic system, IEEE Trans. Ind. Electron., vol. 56, no. 11, pp. 44074415, Nov. 2009.

9. E. Villanueva, P. Correa, J. Rodríguez, andM. Pacas, Control of a single phase cascaded H-bridge multilevel inverter for grid-connected photovoltaic systems, IEEE Trans. Ind. Electron., vol. 56, no. 11, pp. 43994406, Nov. 2009.

10. K. A. Corzine, M. W. Wielebski, F. Z. Peng, and J. Wang, Control of cascaded multilevel inverters, IEEE Trans. Power Electron., vol. 19, no. 3, pp. 732738, May 2004.

11. G. Ceglia, V. Guzman, C. Sanchez, F. Ibanez,Vol. 2 Issue 5, May – 2013

    J. Walter,

    J. Walter,

    and M. I. Gimanez, A new simplified multilevel inverter topology for DCAC conversion, IEEE Trans. Power Electron., vol. 21, no. 5, pp. 13111319, Sep. 2006.

12. V. G. Agelidis, D. M. Baker, W. B. Lawrance, and C. V. Nayar , A multilevel PWMinverter topology for photovoltaic applications, in Proc. IEEE ISIE, Guimäes, Portugal, 1997, pp. 589594.

13. S. J. Park, F. S. Kang,M.H.Lee, and C. U. Kim, Anewsingle-phase fivelevel PWM inverter employing a deadbeat control scheme, IEEE Trans. Power Electron., vol. 18, no. 3, pp. 831843, May 2003.

14. J. Selvaraj and N. A. Rahim, Multilevel inverter for grid- connected PV system employing digital PI controller, IEEE Trans. Ind. Electron.,vol. 56, no. 1, pp. 149158, Jan. 2009.

15. N. A. Rahim and J. Selvaraj, Multi-string five-level inverter with novel PWM control scheme for PV application, IEEE Trans. Ind. Electron., vol. 57, no. 6, pp. 21112121, Jun. 2010.

1. Y. Cheng, C. Qian, M. L. Crow, S. Pekarek, and S. Atcitty, A comparison of diode-clamped and cascaded multilevel converters for a STATCOM with energy storage, IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 15121521, Oct. 2006.

2. Nasrudin A. Rahim, Senior Member, IEEE, Krismadinata Chaniago, Student Member, IEEE, and Jeyraj Selvaraj ,Single- Phase Seven-Level Grid-Connected Inverterfor Photovoltaic System, IEEE Trans. Ind. Electron., vol. 58, no. 6, pp. 2345- 2443, June. 2011