Pure Sinusoidal Interconnection To The Power Grid
Using H-Bridge Multilevel Current-Source Inverter
And Linear Current Compensator
Eka Rakhman Priandana*

Toshihiko Noguchi

Graduate School of Science and Technology
Shizuoka University
Hamamatsu, Japaneka.rakhman.priandana.17@shizuoka.ac.jp

Graduate School of Science and Technology
Shizuoka University
Hamamatsu, Japan
noguchi.toshihiko@shizuoka.ac.jp

Abstract—This paper proposes a new method of gridconnected photovoltaic (PV) system using H-bridge multilevel
current-source inverters (CSI) and a linear current compensator.
The proposed system consists of several H-bridge CSI which areincorporated to generate staircase multilevel current waveform
and a current compensator that generates a linear compensating
current. This battery-driven linear compensating current is thensuperimposed onto the staircase multilevel current waveform inorder to reform the output current to a pure sinusoidalwaveform. As a result, the power grid is fed with a puresinusoidal current waveform and the power quality is being kept
in good condition. The computer simulations confirmed theproposed system is able to deliver power with acceptableefficiency and give outstanding total harmonic distortion by only
using small passive filter.
Keywords—Photovoltaic system; H-bridge multilevel currentsource inverter; linear current compensator; superimposition;
power quality; computer simulations;I.

INTRODUCTION

In distributed power generation applications, especially for
the PV system, the DC power is fed into the grid by using agrid-connected inverter. However, the distributed generation
resources have their own integration issues such asintermittent and unpredictable generation, so they create manystability issues for voltage and frequency. Therefore, theapplication of CSI as a grid-connected inverter for renewableenergy sources gives an alternative solution to solve gridinstability [1].
Since the conduction loss is the main disadvantage of theCSI, in order to achieve an acceptable power efficiency, thecurrent inversion process must employ a fundamental
frequency instead of high switching frequency modulation.
The latter is only needed for the front-end process thatconverts PV output voltage into current with maximum power
point tracking (MPPT) algorithm.
Besides considering the power efficiency, various
international standards such as IEEE-1547, IEEE-929, andEN-61000-3-2, assert requirements on the output power
quality of the inverters. They require the total harmonic
distortion (THD) of the voltage and current have to be below
the specified limits [2].

Battery

PV-1

LinearCurrent
Generator

H-bridge
CSI-1

Im = √2io

Ilinear

Im/M
Point ofCommon
Couplingvo

Co

S1
AC

Load

Im/M

Im/M

Main
Grid

M = (NLEVEL-1)/2

H-bridge
CSI-2

H-bridge
CSI-M

PV-2

PV-M

Figure 1. Proposed system.

The possible solution to solve the problems is by applyinga multilevel technique into CSIs. The method for generating a
multilevel current waveform is by paralleling some H-bridge
CSIs. However, in order to achieve an acceptable power
quality, it requires a current compensator for compensating thecurrent into a pure sinusoidal waveform [3].
As shown in Figure 1, all H-bridge CSIs and linear current
generator outputs are connected to a point of common
coupling (PCC). A small capacitor Co is used for final filtering
the generated currents. Prior to grid-connected process,voltage and frequency of the PV system must be set equallyand in-phase to the main grid with a minimum load assistance.
After being locked by the system’s phase-locked loop (PLL),
the switch S1 connects the main grid to the PV system. Finally,
the PV system may deliver more currents to the heavier load.
This paper summarizes the operation principle and theswitching strategy of the proposed system. Several computer
simulation results are presented on the basis of their measured
quantities.
II.

OPERATION PRINCIPLE AND CONTROL STRATEGY

Figure 2 illustrates the operation principle of the proposedsystem. Each H-bridge CSI generates asymmetrical 3-level
current waveform and then are summed up to result

Figure 2. Operation principle.

Figure 6. 7-level H-bridge hybrid multilevel CSI simulation result.
TABLE I.

LPV IN

Q1
Buck D1
Chopper

D2

OUTPUT

Q2

QD

QC

PV
RETURN

Figure 3. H-bridge current-source inverter module.

symmetrical staircase current waveform. The linear current
generator superimposes the staircase waveform with a linear
current and reforms the output current into a pure sinusoidalwaveform. Figure 3 describes the H-bridge CSI circuit. Itconsists of a buck chopper (Q1, D1, L), a staircase generator
switch (D2, Q2), and a H-bridge (QA-QD). The asymmetrical3-level current waveform generation intends to balance thecurrent stress in the staircase generator switch of each inverter.
Therefore, each inverter consecutively exchanges the duty
cycle of the level every half period of the sinusoidal reference.
In order to generate a linear compensating current, a class-A
linear amplifier with emitter follower configuration is used andcombined with a H-bridge circuit as shown in Figure 4.
Io+-VLIN-QB

QA

Io = VLIN / RSENSEOUTPUT

Figure 4. Class-A amplifier-based linear current generator.
voIL

VREF

+–P-I
ControllerIm–+1/M I
REF

P-I
Controller+–III.

fREF

PLL

Sine
LUT

|ABS|

Staircase
Generator
Switches+H-bridge
Switches

CONCLUSIONREFERENCES[1]
Plant–VLIN

SIMULATION RESULTS

A new method to feed the power grid by using several Hbridge multilevel CSIs with a linear current compensator forthe PV system has been presented with simulation results. Inorder to verify the simulations, the proposed circuit will beinvestigated in hardware experimental setups.

BuckChopper

Zero
Crossing

11-level
83.4 %
0.71 %
1.77 %
0.75 %

Computer simulations have been conducted to verify theproposed system. For comparison purpose, 7-, 9-, and 11-level
configurations were tested. For simulation parameters, each
DC power source voltage is 160 V, the inductor L is 1 mH, thecapacitor CO is 6.8 µF, the load is 10 Ω/1 mH, and the output
voltage is set to 100 V/60 Hz. Figure 6 shows the 7-level ofthe proposed system simulation result. It was confirmed thesmall output capacitor is sufficient to filter the generated
current. Table 1 listed measured quantities of the conductedsimulations. It is shown that the efficiency of the proposedsystem was improving when implemented in higher number oflevels. However, the THD-V was increasing as well but still
below 1%.
IV.

QD

Number of Levels
9-level81.5 %
0.54 %
1.65 %
0.58 %

Figure 5 shows the control scheme of the proposed system.
There are three controllers utilized in the system. First
controller maintains the output voltage vo as well as determines
the current references IREF and linear reference VLIN. The
second one is used for controlling the inductor current IL of thebuck chopper part. And the last one is for grid frequency fo
synchronization. This control scheme is designed to control all
utilized H-bridge CSIs in the PV system.

DC Source

QC

7-level78.4 %
0.44 %
1.69 %
0.49 %

Power Efficiency
THD-I after filtering
THD-I before filtering
THD-VQBQA
Staircase
Generator
Switch+SIMULATION RECORDED DATA.

H-bridge
SwitchesLinearGenerator

foFigure 5. Control scheme of the proposed system.

[2]
[3]

Noguchi, T. and Suroso, “Review of novel multilevel current-source
inverters with H-bridge and common-emitter based topologies,” 2010
IEEE Energy Conversion Congress and Exposition, Atlanta, GA, 2010,
4006-4011.
Suroso and Noguchi, T, “Novel H-bridge multilevel current-source
PWM inverter with inductor-cells,” 2010 Conference Proceedings IPEC,
Singapore, 2010, 445-450.
S. Yamaguchi, T. Noguchi, A. Ikegami, “Hybrid Current-Source
Inverter with High-Efficiency Characteristic and Low-Distortion
Output,” IEEJ Proceedings of Annual Conference, 2013, C4-2.