A Bipolar Pulse Generator With High-Voltage Gain Based on Three-level Neutral-PointClamped Split-Source Inverter

1. A Bipolar Pulse Generator With High-Voltage
Gain Based on Three-level Neutral-Point-
Clamped Split-Source Inverter
1
Report submitted to Dr. Ibrahim Abdelsalam
Done by: Mahmoud Abd Elfattah Mahmoud
ID number: 22223723

2. Abstract
 Bipolar pulse generators represent a key element in various biomedical and industrial applications.
This representation focus on high-voltage bipolar pulse generator based on a split-source neutral-
point clamped (NPC) inverter (SSI).
 The proposed pulse generator provides operation with low input dc voltage while generating output
pulses with a high voltage gain. The boosting action is provided without a dedicated front-end boost
converter, which positively affecting the system cost.
 Analysis of the circuit structure and operational concept is presented on Different versions of the
proposed generator:
 Single module.
 Multimodule.
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3. INTRODUCTION
 PULSE generators applications:
 Water treatment.
 Food industries.
 Biomedical applications.
 The pulse generator can be either unipolar or bipolar.
 The hardware topology of the pulse generator determining the output waveform specifications, such
as amplitude, frequency, and pulse duration.
 Types of pulse generators:
 Marx generator.
 modular multilevel converter (MMC)-based pulse generator.
 full-bridge inverter-based pulse generator.
 non-isolated dc–dc converter-based pulse generators.
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4. PROPOSED PULSE GENERATOR
NPC-SSI pulse generator consists of one leg of the conventional NPC
inverter, which includes:
 Two dc capacitors (C).
 Four insulated gate bipolar transistors (IGBTs) (S1:S4).
 Two diodes (D1 and D2), all rated at half of the inverter dc link
voltage.
 The resistive load (R) is connected between the leg’s midpoint and
the midpoint of dc-link capacitors where the pulsed output
voltage Vo(t) is applied across it.
The input dc voltage (Vin) is connected across the second upper switch
(S2) through proper inductance (L).
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5. Operational States
It divided into three states positive, zero, and negative voltage states.
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6. pulsed output voltage
Where:
 tp is the pulse width.
 T is the periodic time of the bipolar pulsed output.
 VC is the voltage of dc-link capacitors and the magnitude of the pulsed output voltage.
 iL is the inductor current.
The inductor is charged during zero and positive voltage states, while it is discharged during the negative voltage
state. Correspondingly, this results in a high-gain single stage boosting action by utilizing one of the leg switches,
namely, S2. This, in turn, saves employing a front-end boost converter, affecting positively the generator’s cost and
efficiency.
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7. DESIGN AND CONTROL
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A- Gate Pulse Generation:
 Reference voltage is positive, the two upper switches are
turned on (S1 and S2), and the inductor is charged.
 Reference voltage is zero, the second upper switch (S2) and the
first lower switch (S3) are turned on, and the inductor is still
charging.
 Reference voltage is negative, the two lower switches (S3 and
S4) are turned on, and the inductor is discharged.

8. DESIGN AND CONTROL
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B- Input Voltage Vin :
The boosting gain: G =
𝟏
𝟏−𝑫
where D = 𝟏 −
𝒕𝒑
𝑻
→ G =
𝑻
𝒕𝒑
The circuit gain is also defined by: G =
𝟐𝑽𝑪
𝑽𝒊𝒏
G =
𝑻
𝒕𝒑
=
𝟐𝑽𝑪
𝑽𝒊𝒏
→ Vin = 𝟐𝑽𝑪
𝒕𝒑
𝑻

9. DESIGN AND CONTROL
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C- Passive Components Design:
 Inductance:
The inductance should be properly selected to ensure continuous conduction mode.
The relation between inductor current and voltage during charging mode.
Vin = 𝑳
𝒅𝒊
𝒅𝒕
→ L = 𝑽𝒊𝒏
𝑻−𝒕𝒑
Δ𝒊𝑳
where Δ𝒊𝑳 is the peak-to-peak magnitude of the inductor current ripple, which is limited to less
than the inductor average current to ensure continuous conduction mode operation.
iL(ave) =
𝑷𝒊𝒏
𝑽𝒊𝒏
where Pin is the generator input power, ideally equals the generated output power Pout.
Pout =
𝟐𝒕𝒑 . 𝑽𝑪𝟐
𝑻 . 𝑹
=
𝟐 . 𝑽𝑪𝟐
G . 𝑹
=
𝑽𝒊𝒏
𝑽𝑪
𝑹
the average inductor current equal
iL(ave) ≈
Pout
𝑽𝒊𝒏
=
𝑽𝑪
𝑹
inductor value equal
L =
𝑽𝒊𝒏
𝑹
α 𝑽𝑪
𝑻 − 𝒕𝒑
where α = 𝜟𝒊𝑳 / iL(ave)

10. DESIGN AND CONTROL
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 DC-link Capacitances:
It should be selected such that positive pulses are generated
successfully with insignificant voltage droop.
RC ≫ 𝒕𝒑
The proper dc-link capacitance is given by:
C =
𝟐𝟎 𝒕𝒑
𝑹

11. DESIGN AND CONTROL
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D- Voltage Rating of Switches:

12. MULTIMODULE VERSION
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13. MULTIMODULE VERSION
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Operational modes of multimodule version:

14. Case Study
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Output voltage of ±1.5 kV with a pulse width of 15 μs and 1 kHz frequency to be applied across a resistive
load of 1kΩ, the voltage of dc capacitors VC = 1.5 kV. the gain G = 6.67, and the proper input dc voltage is
450 V. The pulsed output current magnitude, iop = VC /R = 1.5 A ∼= iLave. The converter output power =
675 W. If the employed switches have VON = 1.5 V, RON = 3 mΩ, tON = 0.2 μs, and tOFF = 0.3 μs, the total
conduction losses ∼= 3.25 W, while the total switching losses ∼= 19.25 W, i.e., the total losses ∼= 22.5 W.
The overall efficiency ∼= 97%.
Assuming that the rated power is 675 W and the same aforementioned parameters are considered, but
load resistance is changed from 10 to 1 kΩ to check the effect of loading on converter efficiency (where 1
kΩ is the rated load resistance). The efficiency is approximately 97% in the whole operating defined range.

15. SIMULATION
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Simulation Parameters

16. Simulation Results
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17. EXPERIMENTAL VALIDATION
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18. Experimental Results
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Single-module bipolar pulse generator

19. 19
Two-module bipolar pulse generator

20. 20
Three-module bipolar pulse generator

21. 21
ASSESSMENT OF THE PROPOSED PULSE GENERATOR

22. 22
CONCLUSION
an NPC-SSI-based bipolar pulse generator has been proposed for resistive load pulsed applications such as water
treatment and food processing with pulse widths in the microsecond range and repetition rate in the kHz range. The
proposed generator has inherited boosting action with a high voltage gain, which eliminates the need for a front-end
boost converter, positively affecting the generator’s cost and efficiency. Single-module and multimodule versions of
the proposed approach have been presented with the design equations. A ±1.5 kV single-module pulse generator, as
well as a ±4.5 kV multimodule pulse generator with three modules, are simulated to generate pulses with 5 μs width at
a 10 kHz repetition rate. The simulation results validate the presented approach. Scaled-down prototypes are
implemented for validation which are ±65 V single-module pulse generator, ±130 V two-module pulse generator,
±500 V two-module pulse generator, and ±200 V three-module pulse generator. The modules are operated under a 10
kHz repetition rate and generate pulses with 15 µs width. The experimental results follow the proposed approach. The
efficiency of the proposed pulse generator has been investigated where for a bipolar output voltage of ±1.5 kV with a
pulse width of 15 µs and 1 kHz frequency applied across a resistive load of 1 kΩ, the estimated efficiency was 97%, and
the measured average efficiency for the implemented single-module pulse generator was around 98%. Finally, the
proposed bipolar pulse generator has been compared with other bipolar pulse generator alternatives, and the
comparison showed that the proposed generator has a lower component count.