A Hysteresis Current Controller for Single-Phase Three- Level Voltage Source Inverters presented by NITISH KUMAR(M160493EE) APR 4 ,2017 NIT CALICUT

Faculty advisor : Dr. jagadanand g

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CONTENTSINTRODUCTION

OBJECTIVES

HYSTERESIS CURRENT CONTROLLER

REQUIREMENTS AND PURPOSE

MODIFIED SCHEME

FUTURE SCOPE

RESULTS AND CONCLUSION

REFERENCES

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INTRODUCTION To get the desired output voltage in single-phase VSI , we use

Square-wave PWM Single-pulse PWMSinusoidal PWM Modified-sinusoidal PWM

But these type of converter is not having control over output current

When output of inverter have to fed to drives or machines whose torque control is more necessary over other parameters then the necessity of current control comes into the picture.

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OBJECTIVES

To see what is hysteresis current controller

To see how the switching frequency vary with respect to load in the case of hysteresis current controller.

To see how to make it independent from load parameters.

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Why hysteresis current controller

The hysteresis current control technique has proven to be the most suitable solution for applications such as active filters, machine drives, and high-performance converters .

The harmonic performance of a hysteresis current controller can be substantially improved by varying the hysteresis band over each fundamental cycle to maintain a constant switching frequency

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What is hysteresis current controller

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single phase inverter with motor loadAnd block diagram of pulse generator

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Basic requirements and purpose

The basic requirements for the current controllers are low harmonics to reduce losses, low torque pulsation, low noise in the motor, and fast response in order to provide high dynamic performance.

The purpose of a current controller is to control the load currents by forcing them to follow the reference currents.

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mathematical description of switching frequency

When switch 1and 2 conducts,

When feedback diode will conduct, ---L*=0

of switch =

Time period T=

T=

Switching frequency(f)=

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Continued….. Induce EMF in motor drive can be taken as.

f=

f=*()

We can see that the switching frequency of switch is having a constant and a variable component ,this is undesirable.

Though the performance of hysteresis current is very good but the variable switching frequency makes the system complex ,costly and sophisticated.

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MODIFICATIONS IN HCC

Conventional current control has the disadvantage of dependency of switching frequency on load parameter and has a variable switching frequency. So we adapt a new technique for making the switching frequency independent of load parameters like inductance , resistance etc.

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Proposed hysteresis current regulation

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Mathematical description For single phase 3-level inverter If ideal voltage is used for getting

,then For , 2-=L

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Continued …. If V* is assumed constant over the switching period

Using similar triangles, this relationship can be written as: =

By using above equation we can write,

(A)

(B)

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Equation (B) defines the active switching interval required in the next half switching period to precisely restore the inverter operation to a constant switching frequency with centered active pulses.

Equation (A) defines about that hysteresis bandwidth to achieve the same objectives.

Together, these two equations show clearly that there is no difference in principle in using either time or hysteresis bandwidth as a switching control parameter and the selection of either alternative depends only on the hardware used.

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DISADVANTAGE

Additional complex system is required for calculating time and bandwidth for next switching interval in addition to hysteresis current controller

Very fast ADC is required( sampling frequency-25 MHZ)in order to convert the analog domain error to digital domain.

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FUTURE SCOPE

It is having system efficiency of 96.7 percent , so it can further modified to increase the efficiency.

In this case it is showing stable response up to 5 kHz, so it can be further extended for greater frequency.

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RESULTS AND conclusion The proposed method has the following advantages which make it an attractive option for hysteresis current controlled single-phase three-level VSIs:

It has all the benefits associated with hysteresis current control

Switching frequency is constant between two adjacent switched output voltage

Low switching losses

Simple control logic and flexible implementation

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references [1] Huifeng Mao, Xu Yang, Zenglu Chen, Zhaoan Wang , “A Hysteresis Current Controller For Single-Phase Three level Voltage Source Inverters,” IEEE Transaction on power electronics, vol.27, no.7, July 2012

[2] Firuz Zare, Gerard Ledwich, “A Hysteresis Current Control for Single Phase Multilevel Voltage Source Inverters: PLD Implementation,” IEEE Transaction on power electronics, vol. 17, no.5, Sepetmber 2002

[3].G.H. Bode, D.G. Holmes “Load Independent Hysteresis Current Control of a Three Level Single Phase Inverter with Constant Switching Frequency ,”IEEE Transaction on power electronics, 2001

[4].K.M.Rahman, M.Rezwan Khan, M.A.Choudhury, “Variable Band Hysteresis Current Controllers for PWM Voltage-Source Inverter,” IEEE Transaction on Power Electronics,vol. 12, no.6, November 1997 

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