A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

ITOH Junichi

A Novel Engine Generator System with Active Filter and UPS Functions
Using a Matrix Converter
Jun-ichi Itoh, Shunsuke Tamada
Nagaoka University of Technology
1603-1 Kamitomioka-cho
Nagaoka city Niigata, Japan
Tel./FAX: +81/ (258) . 47.9533
E-Mail: itoh@vos.nagaokaut.ac.jp
URL: http://pelab.nagaokaut.ac.jp/itohlab/

Keywords
Matrix converter, Active filter, Regenerating power, Uninterruptible power supplies (UPS), Converter
control

Abstract
This paper proposes the application of a matrix converter to a PM generator for power quality
compensation, such as reactive power compensation, harmonic current and power interruption. The
novel point of this work is that the matrix converter provides reactive power with harmonic current.
Simulated and experimental results confirm that the matrix converter can maintain high performanceas same as a conventional active filter and an uninterruptible power supply (UPS).

I. Introduction
Recently, renewable resources supplies, such as fuel cells, photovoltaic cells, wind power and engine
generators, for distributed power system have been studied intensely. Use of such power supplies
means that power quality compensators, such as active filters, reactive power compensators, anduninterruptible power supplies (UPS) are becoming more important for maintenance of a high quality
power grid.
Power quality compensators with switching devices are constructed based on a voltage source
inverter using six arms. Therefore, conventional power quality compensators require a large
electrolytic capacitor in the dc link part of the equipment. The use of a large capacitor hinders
downsizing efforts and the lowering of equipment costs. In addition, the high reliability is required forthe power compensator and a distributed power system. Therefore the life time of the electrolytic
capacitor causes trouble.
On the other hands, ac to ac direct converters have been studied, such as a matrix converter for motor
drive applications. Direct converters, which do not have a large electrolytic capacitor and an initialcharge circuit, can be used to realize downsizing and lowering of equipment costs, when comparedwith conventional converters. In this case, the input current of the matrix converter is controlled byonly a unity power factor sinusoidal waveform.
This paper proposes the application of a matrix converter to a permanent magnet (PM) generator withpower quality compensation. The input current control response of a matrix converter is higher thanthe conventional voltage type converter, because the input current control works as same as a current
type converter.
A control strategy is also proposed for an active filter with UPS function. The proposed control
strategy is based on a virtual indirect control method [4], which can clearly separate an input side
control and an output side control, such as an indirect matrix converter. Thus, this paper leads a
relation between the input and output current. A compensation capacity of this proposed system isalso mentioned.

EPE 2007 - Aalborg

ISBN : 9789075815108

P.1

A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

ITOH Junichi

Furthermore, simulated and experimental results are provided for reactive power compensation, UPS
operation and active filter operation, using the proposed control method. As a result, the proposedengine generator system has been validated.

II. System Configuration
Figure 1 shows a block diagram of the proposed engine generator system with the matrix converter tocompensate power quality. The reactive power and the harmonics in the power grid are compensatedby the matrix converter, which generates the same reactive power and harmonics as the load.
Assuming that a matrix converter is applied to one type of distributed power supply with a PM
generator, then the matrix converter can supply not only the active power, but also compensate theharmonic current in the power grid, which will realize the maintenance of high power quality without
the use of other active filter equipment.
The energy buffer of the matrix converter is used as a PM generator, instead of a large volume
capacitor. In the case of compensating active power, such as for power interruption and an unbalanced
voltage, a conventional compensator, which consists of a switching device bridge with six arms,
requires a large volume capacitor. However, electrolytic capacitors can not be applied to high voltage
systems, because there are no high-voltage rated electrolytic capacitors.

vs

is

iL

ic
vg
vcf

ic

*

vg

*

Fig. 1. Block diagram for the engine generator system with a matrix converter.

III. Control strategy
A. Virtual indirect control method
The proposed control strategy is based on a virtual indirect control method with a triangular carrier
wave for power grid side control and generator side control, respectively. A feature of this method isthat various control methods for a conventional inverter or rectifier can be applied to a matrix
converter.
The control algorithm is provided by the inverter part (the generator side), the rectifier part (thepower grid side) and a composite pulse width modulation (PWM) generator, which generates thePWM pattern for the matrix converter, as shown in Figure 1. The PWM pattern for the matrix
converter is obtained by the switching functions of the inverter and rectifier part.
Figure 2 and 3 shows a model of the indirect matrix converter and the matrix converter, respectively.
In this case, the relation between the input voltage and the output voltage of the indirect matrix
converter is expressed as⎡ vu ⎤ ⎡ sup⎢v ⎥ = ⎢ s⎢ v ⎥ ⎢ vp⎢⎣vw ⎥⎦ ⎢⎣ swp

EPE 2007 - Aalborg

sun ⎤
⎥ ⎡s
svn ⎥ ⎢ rpsswn ⎥⎦ ⎣ rn

ssp
ssn

⎡vr ⎤
stp ⎤ ⎢ ⎥vsstn ⎥⎦ ⎢ ⎥⎢⎣ vt ⎥⎦

(1)

ISBN : 9789075815108

P.2

A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

ITOH Junichi

where switching function s is defined that s=1 means switch S is turned on, s=0 means switch S is
turned off. Likewise, the relation between the input voltage and the output voltage of the matrix
converter is expressed as⎡ vu ⎤ ⎡ sru⎢v ⎥ = ⎢ s⎢ v ⎥ ⎢ rv⎢⎣vw ⎥⎦ ⎢⎣ srw

ssu
ssv
ssw

stu ⎤ ⎡vr ⎤stv ⎥⎥ ⎢⎢vs ⎥⎥stw ⎥⎦ ⎢⎣ vt ⎥⎦(2).

Therefore, the PWM pattern for the matrix converter can be converted by
⎡ sru
⎢
⎢ srv
⎢⎣ srw

ssu
ssv
ssw

stu ⎤ ⎡ sup⎥ ⎢stv ⎥ = ⎢ svp
stw ⎥⎦ ⎢⎣ swp

sun ⎤⎥ ⎡ srpsvn ⎥ ⎢sswn ⎥⎦ ⎣ rn

ssp
ssn

stp ⎤
⎥
stn ⎦

(3).

Input filter

As a result, control performance of a matrix converter is exactly same as an indirect matrix converter
because the relation between the input voltage and the output voltage is the same. It should be notedthat the relation between the input current and the output current is also the same.

Fig. 2. Indirect converter

r

Sru
Srv
Srw

s

Ssu
Ssv
Ssw

t

Stu
Stv
Stw

u
v
w

Fig. 3. Matrix converter

B. Active filter control with UPS function
Figure 4 shows a control block diagram for rectifier control. This system has two operation modes
for harmonic current compensation such as an active filter, and power interruption compensation suchas UPS. Detection of power interruption is used in the same way as the conventional method, which
detects the magnitude of the input voltage. When a power interruption has occurred, the matrix
converter works as the voltage power source. The selector shown in Figure 1 selects the current
command for UPS mode and active filter mode.

Load current

Selector

iLa
iLb
iLc

p-q
transform

HPF
icq

Capacitor voltage
vcfa
p-q
vcfb
transform
v
cfc

θ

*

vcfp
HPF

icp
+

*

Active power command*of generator

+
?

icp

**

+
?

Kd Kd

icq

inversep-q** transform

Current commandof matrix converter

iap

*

ica
*
icb
*
icc

HPF
vcfq

Fig. 4. Block diagram for rectifier control. Fig. 5. Block diagram for reactive power compensation
with damping control for the input current.
Figure 5 shows a control block diagram for the active filter function. The input current commands
are calculated using the load current. It should be noted that the control method of the rectifier part isEPE 2007 - Aalborg

ISBN : 9789075815108

P.3

A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

ITOH Junichi

the same as a current type converter. In this controller, the load current is converted to a p-q frame,
which is a rotating frame based on the voltage vector of the power grid. Therefore, the values of the paxis represent the active current and those of the q-axis represent the reactive current.
There are two difference points for application of the control method to a conventional power gridcompensator, described as follows:
1) Active power command of the PM generator is added to the active current command.
2) Damping control [5] of the input current is applied to the active and reactive current command
calculation, as shown in Figure 5.
The current commands with damping control are obtained using equation (4). A high pass filter (HPF)
is used to extract the harmonic current from the capacitance voltage. The cut off frequency of the HPF
depends on the harmonics extraction frequency.
***

ic = ic − K dSTv cf
1 + ST(4)

where, ic** is the compensated current command, ic* is the original current command, T is the time
constant, Vcf is the capacitor voltage, and Kd is the damping gain.

C. Input current control method of matrix converter
In this chapter, we discuss the input current control method for the matrix converter based on theindirect matrix converter. The theories of the indirect converter are entirely equivalent to the matrix
converter because the matrix converter is controlled based on the virtual indirect control method inthis proposed system. In this case, for example, when Srp, Stn, Sup, Svp, and Swn are turned on in theindirect matrix converter as shown in Figure 2, R phase is connected to U, V phase, and T phase isconnected to W phase. Likewise, when Sru, Srv, Stw are turned on, R phase is also connected to U, V
phase, and T phase is also connected to W phase in the matrix converter. Thus, the connection
between the input terminal and the output terminal of the matrix converter is the same as converter
indirect matrix converter.
Figure 6 indicates power flow of the indirect matrix converter. The input side converter operates as acurrent source rectifier, and the output side converter operates as a voltage source inverter in theindirect matrix converter. Therefore, the maximum value of the input current depends on magnitude of
the DC link current.

idc

r
s

u
v

edc

t

PM

w

Current source
rectifire

Voltage source
inverter

active powerreactive power

Fig. 6. Power flow of AC/DC/AC converter.
The reactive power of the load side does not affect the DC link stage because the reactive power isgenerated by free wheeling mode. In addition the DC link stage only transmits the active power on theload. It is similar to control a matrix converter with the virtual indirect control method. The indirect
matrix converter does not have an energy buffer. Therefore, the DC link current is determined by theoutput current and the load power factor of the voltage source inverter. The load power factor isEPE 2007 - Aalborg

ISBN : 9789075815108

P.4

A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

ITOH Junichi

calculated using the voltage commands and the output current of the inverter. As a result, the DC linkcurrent is given byiimg _ dc = i out _ max ⋅ cos θ out
v a ⋅ i outα + v β ⋅ i outβ*

= i out _ max ⋅

(vα

*2

*

*2

(5)

+ v β )(i outα + i outβ )22where vα* and vβ* are the output voltage commands of the inverter, ioutα and ioutβ are the output current,

iout_max is the peak value of the output current, and suffix α and β mean on a rest frame.
The control range of the input current is constrained by 3/2 times of the DC link current because
the DC link current has ripple between 3/2i img_dc and iimg_dc. The current source rectifier uses a
triangular carrier in order to generate PWM pulse. Thus, the input current commands are normalizedby 3/2 times of the DC link current. Finally, the modulation index of the input current is obtained by
ic

ic =
**

=

2

*

3
* iimg _ dc
2

⋅

ic

*2

*

3 iout _ max⋅*2(vα + vβ )(ioutα + ioutβ )
2

2

(6)

va ⋅ ioutα + vβ ⋅ ioutβ**

where ic** is the modulation index of the input current, ic* is the input current command.
By using the virtual current source type rectifier with the modulation index as shown in Equation (6),the input current of the matrix converter is able to be controlled by an open loop controller though
there is no auto current regulator for the input side.

IV. Reactive Power Compensation range
The power factor of the input side of the matrix converter deteriorates according to magnitude ofcompensated reactive power, because the input current of the matrix converter not only contain theactive power but also the reactive power to compensate the power grid. As described in previous
chapter, a behavior of a matrix converter can be basically discussed as same as an indirect matrix
converter. In case of an indirect matrix converter, if the input power factor becomes low, then a DC
voltage would decrease. That is, the matrix converter can not control the motor connected to the
output side because the output voltage of the inverter is constrained by the DC link voltage.
Accordingly, we have to carefully choose the reactive power compensated in a load including theoutput voltage of the matrix converter.
In this chapter, we examine the relations between the maximum compensated reactive power and theoutput voltage of the matrix converter. The maximum output voltage of the matrix converter isobtained using
Vout =

3
Vs ⋅ cos θ in2

(7)

where Vs is the power grid voltage, cosθin is the input power factor of the matrix converter.
In case of the indirect matrix converter, the input current of the matrix converter is also depended on
the output power factor and the magnitude of the output current because the input current isdetermined by the DC link current. Therefore, when the matrix converter compensates reactive power,
the input apparent power is obtained using Equation (8).
(8)
S in = Vs ⋅ I out ⋅ cos θ out
where Iout is the output current(RMS), cosθout is the output power factor of the matrix converter.

EPE 2007 - Aalborg

ISBN : 9789075815108

P.5

A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

ITOH Junichi

The input power factor of the matrix converter is given using the apparent power leaded by Equation(8), and reactive power compensated in a load. As the result, the input power factor is obtained using
Equation (9).
S in − Qload2

cos θ in =

=

2

S in

(Vs ⋅ I out ⋅ cos θ out ) 2 − Qload

2(9)

Vs ⋅ I out ⋅ cos θ out

where Sin is the input apparent power of matrix converter, Qload is reactive power for compensation.
Finally, the relation among the output voltage Vout, the reactive power of the load Qload and the load
power factor cos θout for compensation is expressed using Equation (10).
Qload = I out ⋅ cos θ out ⋅ (Vs +23⋅ Vout )(Vs −

2
3

(10)

⋅ Vout )Figure 7 shows the compensation range of reactive power, using Equation (10) under constant output
current Iout and constant input voltage Vs. The ability as a reactive power compensator increases in thedomain of low output voltage and high power factor.
1000

Vs = 200V
Iout = 5A

500

1

0
173

0.5

86

Vout [V]0cosθout

Fig. 7. Compensation range of reactive power.

V. Simulation results
Table 1 shows the simulation parameters used to confirm the basic operation of the proposed system.
The simulation assumes that the commutation of the matrix converter is the ideal, that is, thecommutation time is zero. In this system, the active power is divided between the power grid and the
PM generator. The ratio of the active power (power distribution ratio) between the power grid and the
PM generator is set to almost 7:3.
Table. 1. Simulation parameters.
Power grid voltage

200[V]

Power grid frequency
Carrier frequency
Power distribution ratio(Power grid :PM generator)
LC filter Cut of frequency
LC filter Damping factor
Load(UPS, Active filter operation)

50[Hz]
10[kHz]7:3(reactive power compensation)

EPE 2007 - Aalborg

ISBN : 9789075815108

1.6[kHz]
0.22
Diode bridge(R=75Ω,
DCL=200 mH)
R=25Ω,L=50 mH

P.6

A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

ITOH Junichi

Figure 8 shows the simulation results for reactive power compensation. At the middle of thehorizontal axis, reactive power compensation is initiated and the unity input power factor can then be
obtained. The serving active power of the power grid is decreased, because the PM generator is
supported by the active power. It should be noted that we also confirmed that the proposed system cancompensate the power factor of the power grid for capacitor load.
Figure 9 shows the results for active filter operation, which means harmonic current compensation of
the power grid. The harmonic current causes a diode rectifier. The harmonic compensation is started
in the middle of the horizontal axis. As a result, a good sinusoidal current waveform is obtained in the
power grid. In addition, the simulation results confirm that the damping control can suppress theoscillation of the LC filter to the input current of the matrix converter. However, the oscillation
depends on LC filter in the grid current is slightly remaining.
Figure 10 shows the UPS operation with active filter, which represents power interruptioncompensation by the PM generator system. The output voltage is smoothly changed from the power
grid to the PM generator. The output voltage is controlled by a proportion and integration (PI)controller during the power interruption. That is, the output voltage regulator is immediately applied
when the power interruption occurs. A good sinusoidal voltage waveform is also obtained in this case.

Fig. 8. Simulation results of reactive power compensation with an R-L load

Fig. 9. Simulation results for active filter operation.

EPE 2007 - Aalborg

ISBN : 9789075815108

P.7

A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

200Power grid voltage [V]

ITOH JunichiInterruption

0
-200
5

Power grid current [A]

0
-5
200

Load voltage [V]

0
-200
4

Load current [V]

0
-4
1200

Power of power grid[W]

600
0
0.04

0.14

0.24

time [s].

Fig. 10. Simulation results for UPS operation.

VI. Experimental results
Figure 11 shows the experimental results for reactive power compensation using the proposed system
and RL load. The experimental conditions are almost the same as the simulation, except for the
direction of the power flow, the LC filter design of the matrix converter, and the commutation method
according to the polarity of the input voltage [3]. The experimental setup constrains the operationmode, which is motoring. The input current of the matrix converter controlled as lead phase for the
power grid voltage. As a result, the power factor of the power grid current was corrected as unity.
Figure 12 shows the experimental results for active filter operation for a diode rectifier load. In figure12(a), a good sinusoidal waveform is obtained for the input current of the matrix converter. However,the power grid current contain the distortion due to the input current generates the harmonics
components. On the other hands, in Figure 12(b), the power grid current is compensated by the matrix
converter. As a result, the power grid current becomes a sinusoidal waveform. However, a few
distortion remains in the load current. One of the reasons for the distortion is the influence of voltage
error by commutation.

Fig. 11. Experimental result of reactive power compensation with RL load.

EPE 2007 - Aalborg

ISBN : 9789075815108

P.8

A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

ITOH Junichi(a) Without harmonics compensation.
0
Input voltage [250V/DIV]
0
Input current of matrix converter [5A/DIV]
0
Grid current [10A/DIV]
0
Output current of matrix converter [10A/DIV]

10ms/DIV(b) With harmonics compensation.
Fig. 12. Experimental result of active filter operation.

Fig. 13. Harmonics analysis results of the power grid current.

Figure 13 shows the analysis results of harmonics under the diode rectifier load as shown in Figure
12. The frequency components of 3rd, 5th, 7th and 11th are decreased by applying the proposed
harmonics compensation. However the frequency components of even numbers are higher because
the oscillation of the input current depends on the LC filter causes the current distortion.

EPE 2007 - Aalborg

ISBN : 9789075815108

P.9

A Novel Engine Generator System with Active Filter and UPS Functions Using a Matrix Converter

ITOH JunichiFig. 14. Relation between power factor and THD.
Figure 14 shows the relation between the power factor of the PM motor connected side and the total
harmonics distortion (THD) of the power grid. When the power factor of the PM motor increase,
THD of the power grid becomes low. This means that the compensation is effective according toincreasing the power factor of the PM motor. This reason can be explained as follows. The large
power factor increases the virtual DC link current. As a consequence the input current control range iswidened as discussed in chapter IV. The validity of the analysis is proved because this experimental
result agrees with equation (6).

Conclusion
This paper proposes a new application of the AC/AC direct converter. Reactive power, harmonic
current and power interruption can be compensated by the proposed input current control method of
matrix converter. In addition, this paper described the range of the reactive power compensation,clearly. The proposed compensation strategy is not only applicable to conventional matrix converters,
but it can also be used for an indirect matrix converter with a dc link.
This study was supported by Industrial Technology Grant Program in 2005 from New Energy andIndustrial Technology Development Organization (NEDO) of Japan.

References[1] H. Akagi, “New trends in active filters for power conditioning,” IEEE Trans. Industry Applications, vol.32,
no. 6, Nov/Dec 1996, pp. 1312-1322.
[2] Pichai Jintakosonwit, Hideaki Fujita, Yasufumi Akagi: “Considerations of a Fully-Digital controlled Active
Filter for Installation on Power Distribution Systems” T.IEE Japan, Vol.121-D, No.3 2001 (in Japanese)[3] P. W. Wheeler, J. Rodriguez, J. C. Clare, L. Empringham: ”Matrix Converters: A Technology Review” IEEE
Transactions on Industry Electronics Vol. 49, No. 2, pp274-288, 2002
[4] J. Itoh, I. Sato, H. Ohguchi, K. Sato, A. Odaka and N. Eguchi: “A Control Method for the Matrix Converter
Based on Virtual AC/DC/AC Conversion Using Carrier Comparison Method”, Trans. IEEJ, Vol.124-D, No.5
p457 (2004)[5] Ikuya Satou, Jun-ichi Itoh, Hideki Ohguchi, Akihiro Odaka, Hironori Mine: “An Improvement Method ofMatrix Converter Drives Under Input Voltage Disturbances” International Power Electronics Conference,
Niigata, 546-551, 2005[6] Junnosuke Haruna, Jun-ichi Itoh “A Consideration about the Voltage Utilization Ratio of the Matrix
Converter Connected a Generator to the Input Side”, Annual Conference of IEEJ, No.4-102, 2007(in Japanese)[7] Jun-ichi Itoh, Koji Kato: “Improvement of Commutation Method in Matrix Converter” JIASC2006, 1-O4-1[8] J.Itoh, I.Sato, A.Odaka, H.Ohguchi, K.Kodachi: “A Novel Approach to Practical Matrix Converter Motordrive System with RB-IGBT” Power Electronics Specialists Conference 2004
[9] Yasuhiro Tamai, Sunt Srianthumrong, Hirofumi Akagi: “Comparisons Between a Hybrid Shunt Active Filter
and a Pure Shunt Active Filter”, IEEJ Trans. IA, Vol.124, No.5, 2004

EPE 2007 - Aalborg

ISBN : 9789075815108

P.10