This document presents a hysteresis current controller for single-phase three-level voltage source inverters. Conventional hysteresis current control has variable switching frequency that depends on load parameters, which makes the system complex. The proposed method modifies the hysteresis current controller to make the switching frequency independent of load by dynamically varying the hysteresis bandwidth between switching intervals based on mathematical equations. The results show this method provides constant switching frequency, low switching losses, and simple control logic implementation while maintaining benefits of hysteresis current control.
3. INTRODUCTION
๏ To get the desired output voltage in single-phase VSI , we use
๏ถSquare-wave PWM
๏ถSingle-pulse PWM
๏ถSinusoidal PWM
๏ถModified-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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4. OBJECTIVES
๏ถTo see what is hysteresis current controller
๏ถTo see how the switching frequency vary with respect to load in the case
of hysteresis current controller.
๏ถ To see how to make it independent from load parameters.
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5. Whyhysteresiscurrentcontroller
๏ถThe hysteresis current control technique has proven to be the most
suitable solution for applications such as active ๏ฌlters, machine drives,
and high-performance converters .
๏ถThe 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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8. Basicrequirementsandpurpose
๏ถThe 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.
๏ถ The purpose of a current controller is to control the load currents by
forcing them to follow the reference currents.
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9. mathematicaldescriptionofswitchingfrequency
When switch 1and 2 conducts, ๐๐ = L โ
๐๐ผ
๐๐ก
+ ๐ธ๐
๐๐๐ ๐๐ ๐กโ๐ ๐ ๐ค๐๐ก๐โ =
๐ฟโโ๐ผ
๐ ๐ โ๐ธ ๐
When feedback diode will conduct, -๐๐-๐ธ๐-L*
๐๐ผ
๐๐ก
=0
๐๐๐น๐น of switch =
๐ฟโ๐ผ
๐ ๐+๐ธ ๐
Time period T=๐๐๐ + ๐๐๐น๐น
T=
๐ ๐โ๐ฟโ๐ผ
๐2
๐โ๐ธ2
๐
Switching frequency(f)=๐๐๐๐ฅ โ (1 โ
๐ธ ๐
2
๐ ๐
)
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10. Continuedโฆ..
Induce EMF in motor drive can be taken as.
๐ธ๐ = ๐ โ sin ๐ค๐ก
f=๐๐๐๐ฅ โ (1 โ
๐2โ(sin ๐ค๐ก)2
๐2
๐๐
)
f=๐๐๐๐ฅ*(
1โ๐2
๐2
๐๐
โ
๐2โcos 2๐ค๐ก
๐ ๐๐
)
๏ถWe can see that the switching frequency of switch is having a constant
and a variable component ,this is undesirable.
๏ถ 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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11. MODIFICATIONSINHCC
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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13. Mathematicaldescription
๐๐ผ โ ๐ธ = ๐ฟ
๐๐ผ
๐๐ก
+ ๐ ๐ผ For single phase 3-level inverter
๐โ โ ๐ธ = ๐ฟ
๐๐ผโ
๐๐ก
+ ๐ ๐ผโ If ideal voltage ๐โ is used for getting ๐ผโ
๐ โ ๐โ
= ๐ฟ
๐๐ผ ๐
๐๐ก
๐ก1,๐,then ๐โ
= ๐ฟ
๐ต1
๐ก1,๐
For ๐ก1,๐ด, 2๐๐๐-๐โ
=L
๐ต1
๐ก1,๐ด
๐โ = 2๐๐๐
๐ก1,๐ด
๐ก1,๐+๐ก1,๐ด
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14. Continued โฆ.
If V* is assumed constant over the switching period
๐1
โ
= 2๐๐๐
๐ก1,๐ด
๐ก1,๐+๐ก1,๐ด
= ๐2
โ
= 2๐๐๐
๐ก2,๐ด
๐ก2,๐ด+๐ก2,๐
Using similar triangles, this relationship can be written as:
๐ก1,๐
๐ก2,๐
=
๐ก1,๐ด
๐ก2,๐ด
=
๐ต1
๐ต2
=
๐1
๐2
By using above equation we can write,
๐ต2 = ๐ต1
โ๐โ๐ฟ๐ก2
โ๐+๐ฟ๐ก2โ๐ฟ๐ก1
(A)
๐ก2,๐ด = ๐ก1,๐ด
โ๐โ๐ฟ๐ก2
โ๐+๐ฟ๐ก2โ๐ฟ๐ก1
(B)
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16. ๏ถ 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.
๏ถ Equation (A) defines about that hysteresis bandwidth to
achieve the same objectives.
๏ถ 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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17. DISADVANTAGE
๏ถAdditional complex system is required for calculating time and
bandwidth for next switching interval in addition to hysteresis current
controller
๏ถVery fast ADC is required( sampling frequency-25 MHZ)in order to
convert the analog domain error to digital domain.
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18. FUTURE SCOPE
๏ถIt is having system efficiency of 96.7 percent , so it can further
modified to increase the efficiency.
๏ถIn this case it is showing stable response up to 5 kHz, so it can be
further extended for greater frequency.
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19. RESULTSANDconclusion
The proposed method has the following advantages which make it an
attractive option for hysteresis current controlled single-phase three-
level VSIs:
๏ถIt has all the bene๏ฌts associated with hysteresis current control
๏ถSwitching frequency is constant between two adjacent switched
output voltage
๏ถLow switching losses
๏ถSimple control logic and ๏ฌexible implementation
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20. references
[1] Huifeng Mao, Xu Yang, Zenglu Chen, Zhaoan Wang , โA Hysteresis Current Controller For Single-
Phase Three level Voltage Source Inverters,โ IEEE Transaction on power electronics, vol.27, no.7, July
2012
[2] Firuz Zare, Gerard Ledwich, โA Hysteresis Current Control for Single Phase Multilevel Voltage
Source Inverters: PLD Implementation,โ IEEE Transaction on power electronics, vol. 17, no.5,
Sepetmber 2002
[3].G.H. Bode, D.G. Holmes โLoad Independent Hysteresis Current Control of a Three Level Single
Phase Inverter with Constant Switching Frequency ,โIEEE Transaction on power electronics, 2001
[4].K.M.Rahman, M.Rezwan Khan, M.A.Choudhury, โVariable Band Hysteresis Current Controllers for
PWM Voltage-Source Inverter,โ IEEE Transaction on Power Electronics,vol. 12, no.6, November 1997
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