Implementation of Cascaded H-Bridge Multilevel Inverter using MATLAB-DSP ( ezDSP 28335 ) Interfacing

This study demonstrates, the generation of triggering signals using SPWM technique for a seven level HBridge cascaded inverter with the help of MATLAB-DSP (ezDSP 28335) interfacing without using EPWM block and presents the final output of the inverter. The focus is mainly on hardware implementation of Cascaded H-Bridge MLI using MATLAB-DSP interfacing. Generation of triggering signals using MATLAB-DSP interfacing has been explained briefly. Use of GPIO block in SIMULINK model makes the triggering signal generation easier and more efficient. The switching control signals required for triggering of switches are generated using MATLAB-DSP (ezDSP 28335) interfacing. This approach exploits the advantages of block programming in SIMULINK.


INTRODUCTION
The increasing number of sensitive loads on electrical utility requires high power quality.Also for medium voltage grid it is troublesome to connect only one power semiconductor switch directly (Tolbert et al., 1999;Tolbert and Peng, 2000).Multilevel Inverters (MLIs) have been developed to fulfill these requirements.Several topologies have been developed during the last two decades.Some of these topologies are: • Cascaded H-Bridge MLI • Diode clamped • Flying capacitors Multilevel inverter synthesizes stepped output voltage nearly equal to sine wave using single or multiple DC sources (Tolbert et al., 1999;Peng and Qian, 2003).Traditionally, the multi-pulse inverter comprising of several Voltage Source Inverters (VSIs) connected together through zigzag arranged transformers were used.But these transformers are expensive, inefficient, occupy large area and are prone to failure.Multilevel inverters were first introduced in 1975 as a solution to the above problem.The terms multilevel were first used for three level and further many topologies have been discovered.Three major topologies are: • Cascaded H-Bridge MLI • Diode clamped or Neutral clamped • Flying capacitors or Capacitor clamped (Rodríguez et al., 2002;Sadigh and Barakati, 2012;Beser et al., 2008) Among these three topologies mentioned above the Cascaded H-Bridge is simplest (Ali Khajehoddin et al., 2007).In this structure M-level output is synthesized using (M-1) /2 H-bridges.Each H-Bridge has its own isolated DC source.The cascaded single phase 7-level inverter as shown in Fig. 1 has ((7-1) /2 = 3) three H-Bridges with three isolated DC sources (Peng and Lai, 1997;Sujitha and Ramani, 2012).The Cascaded MLI: • Eliminates the bulky transformers required in multi-pulse inverter • Can generate almost sinusoidal waveform • Has fast dynamic response Due to its simple and modularized structure it can be made up to unlimited number of levels.This inverter has low cost, high performance, less electromagnetic interferences and higher efficiency than traditional multi-pulse inverter (Liu and Leng, 2012).It can reduce dv/dt stress; thereby electromagnetic compatibility problem can be reduced (Rokan et al., 2010).
In the recent years several strategies and control methods have been developed for switching the devices in the H-bridge (Peng and Qian, 2003;Lesan et al., 2009).Some of them are sinusoidal Pulse with Modulation (SPWM), Selective Harmonics Elimination (SHE-PWM), Space Vector Modulation (SVM) and others (Holmes and Lipo, 2013;Zafarullah Khan et al., 2009).Each method has its own benefits and short comings.This study demonstrates, the generation of triggering signals using SPWM technique for a seven level H-Bridge cascaded inverter with the help of MATLAB-DSP (ezDSP 28335) interfacing without Fig.1: Single phase 7-level inverter using EPWM block.Further the Real Time Workshop (RTW), a SIMULINK add-on software, which automatically generates C and ADA codes from SIMULINK model, allows the integration of a simulation software to the development environment (Pop et al., 2004).The system designer can the algorithm using SIMULINK blocks and convert these blocks in to executable binary codes in C or Assembly language using RTW.

SPWM
generation using MATLAB interfacing: Generation of triggering signals using DSP for the control of voltage source inverters has helped substantially in the development of electric drives used in many industrial applications (Hercog Although there are several ways of generating the Further the Real Time Workshop on software, which automatically generates C and ADA codes from SIMULINK model, allows the integration of a simulation software to the development environment 2004).The system designer can implement the algorithm using SIMULINK blocks and convert these blocks in to executable binary codes in C or

SPWM
generation using MATLAB-DSP Generation of triggering signals using DSP the control of voltage source inverters has helped substantially in the development of electric drives used in many industrial applications (Hercog et al., 2003).Although there are several ways of generating the triggering signals using DSP, the one using DSP interfacing has its own advantages.SIMULINK is MATLAB add-on software which allows block programming.Hence, the system designer can simply use the blocks to implement the algorithms rather than giving more time in developing codes.Further th Time Workshop (RTW), a SIMULINK add software, which automatically generates C and ADA codes from SIMULINK model, allows the integration of a simulation software to the development environment.The system designer can implement the algorithm using SIMULINK blocks and convert these blocks in to executable binary codes in C or Assembly language using RTW.Subsequently these codes are executed in Code Composer Studio (CCSV 3.3), DSP software and downloaded in to the connected DSP processor.The outputs can be taken out from the pins available on the DSP processor board.In the case of signal generation for triggering H Sine-wave Pulse Width Modulation (SPWM) can be generated easily using EPWM block available under the target preference blocks section in SIMULINK to the limited number of EPWM pins, in pins which are available in ezDSP 28335 board makes its unsuitable for the higher level H Hence, another approach to generate SPWM for triggering 7-level H-bridge is described stepwise in the following section.

Triggering signal generation for single phase 7 H-bridge:
Step 1: Connect the ezDSP 28335 processor to cc studio.Open MATLAB and type in the workspace and press enter.The connected DSP processor name will be displayed in the workspace.
Step 2: Connect the blocks as shown in Fig. 2 Step 3: Change the sine wave block parameters, sine type to sample based.Give sample per period as 100 and sample time as 0.0002 for a 50 Hz signal.The amplitude of sine wave is kept 2.5.The repeating sequence stair is given parameters such as to give a discretized up down triangle such as vector of output values is changed to (0 0.5 1 1.5 2 2.5 3 3 2.5 2 1.5 1 0.5 0) and sample time is change for approximately 1.5 kHz switching frequency.The resulting simulation output is shown in Fig. 3. Which shows the triggering pulse for the positive half cycle of a two level inverter.
The hardware output can be taken out from t GPIO0 pin (p8-9 th pin and ground pin (p8 DSP processor.Figure 4 shows the DSO output of the above simulation out of the DSP kit for both positive and negative half cycles of a two triggering signals using DSP, the one using MATLAB-DSP interfacing has its own advantages.SIMULINK is on software which allows block programming.Hence, the system designer can simply use the blocks to implement the algorithms rather than giving more time in developing codes.Further the Real Time Workshop (RTW), a SIMULINK add-on software, which automatically generates C and ADA codes from SIMULINK model, allows the integration of a simulation software to the development environment.The system designer can implement the SIMULINK blocks and convert these blocks in to executable binary codes in C or Assembly language using RTW.Subsequently these codes are executed in Code Composer Studio (CCSV 3.3), DSP software and downloaded in to the connected DSP s can be taken out from the pins available on the DSP processor board.In the case of signal generation for triggering H-bridge switches, wave Pulse Width Modulation (SPWM) can be generated easily using EPWM block available under the SIMULINK.But due pins, in EPWM output pins which are available in ezDSP 28335 board makes its unsuitable for the higher level H-Bridge application.Hence, another approach to generate SPWM for bridge is described stepwise in the  values parameter in repeating sequence stair block is changed to (0 0.2 0.4 0.6 0.8 1 1 0.8 0.6 0.4 0.2 0) for 1 complementary 4 th signal for the negative cycle, (1 1.2 1.4 1.6 1.8 2 2 1.8 1.6 1.4 1.2 1 for 2 nd signal and its complementar for the negative cycle and 3 2.8 2.6 2.4 2.2 2) for 3 complementary 6 th signal for the negative cycle.The Digital output block is configured for six different pins say GPIOx (x = 0, 1, 2, 3, 4, 5).
Step 5: Build the model in SIMULINK convert the model in to C and Assembly language code files.Automatically a project of the same name as that of will be created in CC Studio and it is built and downloaded automatically in the DSP processor.Now, the simulation and the hardware output of the triggering signals for 7 level H-Bridges can be seen as shown in Fig. 6  and 7.

RESULTS AND DISCUSSION
The triggering signal output of DSP is used to trigger the switches in the H-bridges.The model for 7-level H-bridge, connected to the above generated signal, is shown in Fig. 8 the figure there are three bridges each consisting of four switches and have isolated DC supplies.The first and fourth signals from the top, shown in Fig. 6: Simulation output of triggering signals values parameter in repeating sequence stair 0 0.2 0.4 0.6 0.8 1 1 0.8 for 1 st signal and its signal for the negative 1 1.2 1.4 1.6 1.8 2 2 1.8 1.6 1.4 1.2 1) signal and its complementary 5 th signal for the negative cycle and (2 2.2 2.4 2.6 2.8 3 for 3 rd signal and its signal for the negative cycle.The Digital output block is configured for six different pins say GPIOx (x = 0, 1, 2, 3, SIMULINK.This will convert the model in to C and Assembly language code files.Automatically a project of the same name as that of SIMULINK model Studio and it is built and downloaded automatically in the DSP processor.Now, the simulation and the hardware output of the triggering signals for 7-Bridges can be seen as shown in Fig. 6 RESULTS

AND DISCUSSION
The triggering signal output of DSP is used to bridges.The SIMULINK bridge, connected to the above 8.As can be seen in the figure there are three bridges each consisting of four switches and have isolated DC supplies.The first and fourth signals from the top, shown in Fig. 6, are given Figure 10 shows the hardware setup for the project.The picture has desktop and DSP kit for the MATLAB DSP inter facing, the set of opto-couplers for isolation and bridges for the inverter circuit.Both the bridges and the opto-couplers are given supply from the Regulated Power Supplies (RPS).
The outputs of both the simulation model and hardware circuit is shown in Since it has many input/output ports it allows to go for higher levels.This inverter is suitable for electric vehicle drives, utility interface for renewable energy sources, voltage regulation and phase shifting, reactive power control and compensation, high quality power supply etc. pulse inverter, diode clamped and flying capacitor eration of triggering signals using DSP interfacing has been explained briefly.
SIMULINK model makes the triggering signal generation easier and more efficient.
Since it has many input/output ports it allows to go for els.This inverter is suitable for electric vehicle drives, utility interface for renewable energy sources, voltage regulation and phase shifting, reactive power control and compensation, high quality power Triggering signal generation for single phase 7-levelConnect the ezDSP 28335 processor to cc studio.Open MATLAB and type ccsboardinfo in the workspace and press enter.The connected DSP processor name will be displayed in the workspace.Connect the blocks as shown in Fig.2.Change the sine wave block parameters, sine type to sample based.Give sample per period as 100 and sample time as 0.0002 for a 50 Hz ignal.The amplitude of sine wave is kept 2.5.The repeating sequence stair is given parameters such as to give a discretized upsuch as vector of output values 0 is changed to 0.00005 for approximately 1.5 kHz switching frequency.The resulting simulation output is Which shows the triggering pulse for the positive half cycle of a two levelThe hardware output can be taken out from the pin and ground pin (p8-19 th ) of the 4 shows the DSO output of the above simulation out of the DSP kit for both positive two level inverter.For

Fig. 7 :
Fig. 7: Hardware output of triggering signals for three H Fig. respectively.CONCLUSION Hardware implementation of Cascaded H MLI topology using MATLAB-DSP interfacing has been proposed.Easy modularization and packaging of this inverter solve the problem of conventional multi bridge switches respectively of the first bridge, second and fifth signals are given to the diagonal switches respectively of the second bridge, similarly third and sixth signals are diagonal switches respectively of the third bridge.The individual outputs cascade.The hardware connection of the simulation described above has similar structure except some small block diagram of the 9.The first block represents the triggering signals generation through DSP.The second block is the only modification in the hardware connection from that of in simulation.This is the isolation required to protect the low voltage part from the irregularities of the high voltage part.For this 250 as an isolator.This IC converts the signals from DSP kit in to optical signals and again the optical signals are converted back to the electrical form.Hence the low and high voltage sides are not electrically connected but optically isolated.The third and fourth blocks represent bridges model.shows the hardware setup for the project.The picture has desktop and DSP kit for the MATLABcouplers for isolation and bridges for the inverter circuit.Both the bridges and couplers are given supply from the Regulated The outputs of both the simulation model and hardware circuit is shown in Fig. 11 and 12 are implementation of Cascaded H-bridge DSP interfacing has been proposed.Easy modularization and packaging of this inverter solve the problem of conventional multi-pulse inverter, diode clamped and flying capacitor inverter.Generation of triggering signals using MATLAB-DSP interfacing has been explained briefly.Use of GPIO block in SIMULINK triggering signal generation easier and more efficient.