Stabilized Power AC-DC-AC Converter using Different Type of Passive Filters

Stabilized Power AC-DC-AC Converter using Different Type of Passive Filters

ISSN: 2278-0181

Ashok Singroly with the Electrical & Electronics Engineering Department, IES College of Technology Bhopal

Vol. 1 Issue 6, August – 2012

Abstract Passive filters are used to filter the specific harmonics from AC voltage/current waveform and to reduce the ripple contents in DC voltage/current. Different filter topologies in converter fed loads may be C, LC, LCL or a combination of these. The basic criteria to design of such filters are based on analysis of the harmonic frequencies generated by the conversion system. In this paper, design methods for AC and DC side filters in AC-DC-AC converters are presented to optimize the size of filter components to optimize the filter cost and system performance. The performance of the filter designed are verified by simulation in terms of voltage/current THD, ripple content in DC voltage, fundamental value of voltage/current and RMS value of output voltage/current. LCL filters given the better performance.

Keywords Passive filters, LC- filter LCL-filter, L + LC- filter.

I

1. INTRODUCTION

   ncreased use of the nonlinear and time varying devices has led to distortion of voltage and current waveforms. As a consequence, recently the issue of power quality has become important. Both electric utility and end users of electric power are becoming increasingly concerned about the quality of electric power. The term power quality has been used to describe the variation of the voltage, current

   and frequency on the power system beyond a limit .

   Most recent problems involve electronic equipment that is very sensitive to pollution of power line. In the presence of harmonics, equipments such as computers, telephone systems, and controllers may respond incorrectly to normal inputs, not respond at all, or give false outputs. Following are the detrimental effects of harmonic injection into the utility

   1. Excessive losses and heating in motors, capacitors and transformers connected to the system,

   2. Insulation failure due to the overheating and over voltages,

   3. Overloading and overheating of the neutral conductors with loss of conductor life and possible risk of fire.

   4. Malfunctioning of sophisticated electronic equipments,

   5. Interference with the communication network.

   Restrictions on current and voltage total harmonic distortions are being maintained in many countries according to IEEE 519-1992, IEC 61000-3-2/IEC 61000-3-

   4 standards. Various standards are set to limit the harmonics generated by nonlinear loads. The 5% voltage distortion

   limit was recommended below 69 kV, while the limit on current distortion is fixed in the range of 2.5% to 20%

   depending upon the size of the customer and the system voltage. The available harmonic reduction techniques are based on passive components, mixing single and three- phase diode rectifiers and PWM techniques such as active filters, multi-pulse rectifiers and PWM rectifiers.

   In this paper, design methods for AC and DC side filters in AC-DC-AC converters are presented to optimize the size of filter components to optimize the filter cost and system performance. The performance of the filter designed are verified by simulation in terms of voltage/current THD, ripple content in DC voltage, fundamental value of voltage/current and RMS value of output voltage/current.

   The effect in output current, output voltage, and supply current and ripple in dc component with different values of capacitor and inductor have been presented.

2. CLASSIFICATION OF PASSIVE FILTERS

   A different type of passive filters is used in ac-dc-ac converter they may be classified as:

   1. D.C. Passive Filters

      Capacitive D.C. Filter Inductive D.C. Filter

      Inductive & Capacitive D.C. Filter

   2. A.C. Source Side Passive Filters

      A.C. Shunt Filter

      Single Tuned &High Pass Filter

      A.C Series Inductive & Capacitive Filters

   3. A.C. Inverter Side / lode side Filters

   LC filter LCL filter L+LC-filter.

3. DESIGN CRITERIA OF PASSIVE FILTERS

   (a.) Capacitive D.C. Filters

   A DC choke and an electrolytic capacitor bank on the DC bus filter the voltage and the current ripples and improve the input power factor. Capacitor and choke values are derived to optimize overall filter performance [1].

   The design sequence for the filter consists of the following steps:

   Steps 1 – Calculate the capacitance needed to manage a certain level of ripple voltage: for a depiction of the rectifier output waveform. The peak ripple voltage (V max) is first calculated

   V max = Vrms x. 2

   If the maximum acceptable ripple voltage is 80 volts, then Vmin = Vmax – Vripple

   A calculation is made assuming all the energy is taken

   Cr=

   1 (6f)2Lr

   from the capacitor. The energy in a capacitor is typically defined as 1/2 x C xVmax. Based on this formula the following calculation can be made

   The passive elements of series harmonic filter selected on the basis of resonating frequency Compensating capacitor is selected such that the input power factor at the

   min

   P load = (1/2 x Cdc x V2 max -1/2 x Cdc x V2

   ) /t watts

   rated output reaches its maximum value

   D3

   D1

   A capacitor load bank can be made up several ways. We have chosen to use a capacitor value of 500uf to 10000uf for 500 V.

   Step 2 – Calculate the ripple factor of DC voltage from the AC Line and from load

   Lr

   Lr

   A Cr

   B

   Lr

   C

   Cr

   Ldc

   D5

   Cdc

   R

   VO L

   D6

   D4

   D2

   Ripple factor RF=Vac / Vdc

   Step 3 calculate the ripple voltage .

   (b.)A.C. Shunt source side Filter

   Three-phase harmonic filters are shunt elements that are used in power system for decreasing voltage distortion and for power factor correction. In order to achieve an acceptable distortion, several banks of filters of different types are usually connected in parallel. consists of tuned LC filters and/or high pass filters are used to suppress the harmonics. The shunt passive filters are tuned most of the time on a particular harmonic frequency to be eliminated. So that it exhibits low impedance at the tuned frequency

   .

   Fig 2. AC-series Inductive-Capacitive Filter

   (c.) A.C. Inverter Side / lode side Filter:

   (i) LC filters design:

   The simplest filter is the single section LC filter .The series elements an inductance and the shunt element a capacitance. In the series inductance, harmonics voltages are developed and harmonics current flow through the shunt capacitance.. The load power factor should be considered in selecting the individual values of L and C

   Resonance frequency

   than the source impedance, to reduce the harmonic current flowing into the source.i.e. The filtering characteristics are determined by the impedance ratio of the source and passive filter. The most commonly used A.C. shunt filters are:

   1. Single tuned shunt LC:

      D1

      These are used to filter lowest order harmonics such as

      3phase 440v

      50 hz a.c. supply

      Ldc

      D3

      D5

      D6

      Cdc

      fres=

      Q1 Q3

      Vdc

      1

      2LC

      Q5

      L1

      L1 RL

      a.c.

      L1 load

      5th, 7

      th, 11

      th, 13

      th, etc. Band-pass filters can be tuned at a

      D2 Q4

      Q6 Q2

      C1 C1 C1

      singe frequency (single-tuned filter) or at two frequencies (double-tuned filter) as shown in Fig.(1)

      D4

      Fig 3 A.C. Inverter side filter

      single tuned filter Lac

      Cac

      High

      pass filter

      Lac

      R

      Cac

      Cac Cac

      R R

   2. LCL-filter design:

   A topology of an LCL-filter used is seen in fig 4. The LCL-filter is currently probably the most widely used topology. The reason for the popularity of the LCL filter is that good attenuation is achieved with a relatively small component values .i.e, good power quality is achieved with a reasonable filter costs. To find the desired resonance frequency, the filter parameters must be optimized.

   D1

   Ldc

   D4

   Fig 1 single tuned & high pass Shunt LC Filter

   3phase 440v

   50 hz a.c. supply

   D5

   D6

   D3

   Cdc

   Q1 Q3 Q5

   L1 L2

   RL

   load

   L1 L2

   L1 L2

   Vdc

   1. High-pass filters:

      D2 Q4

      Q6 Q2

      C1 C1 C1

      Which are used to filter high-order harmonics and cover a wide range of frequencies. A special type of high-pass filter, the C-type high-pass filter, is used to provide reactive power and avoid parallel resonances as shown in Fig (1).

   2. AC-series Inductive-Capacitive Filter:

   Fig 4. A.C. Inverter Side LCL filter

   By taking the resonance frequency fres to be the primary design parameter, we are able to set the resonance frequency without having to iterate it. The resonance frequency of the LCL-filter is defined as

   Inductive element (Lr) of series filter is chosen so that

   fres

   1 .. L1

   L2 ……….. ………. ………(1)

   the inductive element should not be bulky capacitive element (Cr) of series filter can be selected as:

   2 L1L2C

   No. of harmoni c	without filter	5th arm filter	7th arm filter	high pass filter	5th&7t h filter	sourc e side filter
   5th	16.49	0.02	15.5 4	13.24	0.02	0.01
   7th	9.78	6.51	0.01	8.61	0.01	0.01
   11th	6.56	4.51	5.61	4.86	3.32	2.31
   13th	5.08	3.5	4.38	2.81	2.6	1.37
   Total	22.23	10.2	18.5	17.50	5.99	3.65
   THD%

   If the capacitor value is fixed and the antiresonance frequency is known, then the inductance L2 can be calculated as

   L2 1 ..

   2

   1 ..

   2 resC

   L1………. ……….

   Eq(5)

   fres

   1 .. 1

   r ……….. ………. ………. . (2)

   If the value of the inductor L2 is chosen instead, then the value of the capacitor could be calculated using Eq.(5) first, by solving C.

   Method using resonance frequency as design parameter :

   2 rL1C

   res 1

   Then by selecting the desired capacitor values, fres as a function of the inductor ratio r = L2/L1 can be obtained. The resonance frequency in Eq. (2) can be presented as 2 L C

   = 1+ r and the capacitor value C=1+r/Wres 2L1 .

   (iii) L+LC-filter design:

   The difference between the LCL-filter and the L+LC- filter is that the L+LC-filter has two resonance frequencies while the LCL-filter has only one. Actually, the LCL-filter has three resonance frequencies, but the one defined by.(2) is the essential from the practical viewpoint. The two resonance frequencies of the L+LC-filter are called the antiresonance frequency fares and the resonance frequency fres due to the nature of resonances. At the antiresonance frequency the frequency components of the line current are attenuated whereas at the resonance frequency they are amplified.

   Ldc

   The first step, again, is to choose the value for the capacitance. Then by assuming the parallel connected inductance L1||L2 to be equal to inductance L1, the inductance L2 can be solved from Eq.(4). When L2 is solved and substituted in Eq. (5), the value for inductance L1 is obtained. When all parameters are solved, the resonance frequencies could still be inappropriate. To get the frequencies match with the frequencies specified, some iteration has to be done.

   Type of filter	Capacitive filter	Inductive filter	Ldc & Cdc filter
   Ripple voltage (volt)	60 (10%)	80 (13%)	3.2 (0.5%)

4. COMPARATIVE EVALUATION OF PASSIVE FILTERS

   1. D.C Filter:

      Table 1 show the comparison of D.C. filter capacitive filter is used ripple free dc voltage ,inductive filter is used

      3phase 440v

      a.c.

      Q1 Q3 Q5

      D3

      D1

      D5

      D6

      D4

      Vdc

      L1

      L1 RL

      a.c.

      for smooth the supply current ,Ldc& Cdc filter are used for compensating of voltage as well as current & ripple voltage is also reduce 3.2 volt. Main object of dc obtain ripple free

      50 hz

      supply

      Cdc

      D2

      L1

      L2

      Q4 Q6 Q2

      C1

      load

      constant DC output voltage & continuous output current.

      Table 1 comparison of different type of D.C.filter

      Fig 5. A.C. Inverter Side L+LC filter

      The antiresonance frequency is placed on the switching frequency. When placing the resonance frequency of the L+LC-filter, a couple of things should be considered. a considerable loss of attenuation occurs when the ratio between the antiresonance fares and the resonance

   2. A.C. Source Side Filter :

      In shunt source side filter the THD of the supply current is reduced to well below 5% (22% to 3.65%) & the fundamental value of supply current will be increase further by eliminating the ac inductor and increasing dc capacitance of the rectifier, the rectifier current would increase larger,

      fares

      1 ..

      2

      1 ………. ………. ……….

      L1 L2 C

      frequency fres

      kL+LC=ares/res is diminished.

      which may result in over current to the rectifier.

      Table 2 Comparing of Different Type of A.C. Source Side Filter with Specified nth Order of Harmonic

      In other words, the higher the resonance frequency is

      compared to the antiresonance frequency; the lower is the attenuation on the higher frequencies.

      When only the L+LC-filter is considered, the resonance frequencies could be characterized as the serial and the parallel resonance of the filter. That is, the antiresonance frequency could be calculated as and the resonance frequency as

   3. Inverter Side Ac Filter:

   Filter parameters of LC, LCL- and L+LC-filters using the component values fulfill the requirement for the line voltage distortion (THD < 5 %) at constant switching frequency.

   Eq(3)

   fres 1 ..

   2

   1

   L2C

   ………. ………. ……….Eq (4)

   vof o/p voltage

   Types of filter		Vo output voltage(volt)		Io output current(amp)
   		Vo without filter	Vof with filter	Io withou t filter	Iof with filter
   LC filter	Fund. value	573.8	567.4	21.29	22.95
   	R.M.S.value	405.7	401.2	15.02	16.23
   	THD (%)	44.63	4.71	30.69	0.59
   LCL filter	Fund. value	575	565.9	21.04	22.89
   	R.M.S.value	406.7	400.2	14.88	16.19
   	THD (%)	44.63	3.63	30.21	0.45
   L+LC filter	Fund. value	575.2	565.5	22.23	22.88
   	R.M.S.value	406.7	400	15.72	16.18
   	THD (%)	44.63	4.7	25.19	0.63

   500

   0

   -500

   vof o/p voltage with filter

   vof o/p voltage

   500

   0

   -500

   vof o/p voltage with filter

   Table 3. Comparison of different types of inverter side A.C. filters

   0.4 0.405 0.41 0.415 0.42 0.425 0.43 0.435

   Time (s)

   Fundamental (50Hz) = 565.9 , THD= 3.63%

   Mag (% of Fundamental)

   100

   80

   60

   40

   20

   0

   0 10 20 30 40 50

   Harmonic order

   0.4 0.405 0.41 0.415 0.42 0.425 0.43 0.435

   Time (s)

   Fundamental (50Hz) = 565.5 , THD= 4.73%

   Mag (% of Fundamental)

   100

   80

   60

   40

   20

   0

   0 10 20 30 40 50

   Harmonic order

5. CONCLUSION

Filter design methods presented, revealed some important issues that should be noticed while designing a filter for PWM voltage source converter. In particular, it was shown that the simulation result when an LCL filter is used for the PWM inverter has a major impact on the performance of the filter.

The performance comparison between LC,LCL ,L+LC filter in the term of component size ,shower very clearly the superior performance of the LCL filter over the other filter .

120

100 o/p volt thd before filter

o/p volt.THD(%)

LC filter

(c)With LCL filter (d) With L+LC filter

APPENDIX

Simulation Parameter Of Shunt & Series Filter. A.C. Source Side Shunt Filter.

Simulation t Parameter of Inverter Side A.C .Filter

80 LCL FILTER

L+LC FILTER

60

40

20

0

0 10 20 30 40 50 60

capicantance inuf

Fig 6.Effect of capacitor value of output voltage THD (%) For different type A.C inverter filter

Simulation result of inverter side A.C. filter:

REFERENCES

1. Pasi Peltoniemi, Riku Pöllänen, Markku Niemelä and Juha Pyrhönen, Comparison of the Effect of Output Filters on the Total Harmonic Distortion of Line Current in Voltage Source Line Converter Simulation Study Department of Electrical Engineering, Lappeenranta University of Technology, Lappeenranta

   voi o/p voltage in volt

   500

   0

   -500

   Vo output voltage without filter

   vof o/p voltage

   500

   0

   -500

   vof o/p voltage with filter

   FIN-53851 W.-K. Chen, Linear Networks and Systems (Book style). Belmont, CA: Wadsworth, 1993, pp. 123135.

2. F.Z.Peng, H.Akagi, A.Nabae, A Novel Harmonic Power Filter ,

   IEEE PESC '88 Record (April 1988) pp(1151-1158)

3. Per- Anders Gath, RIFA Electrolytics AB Sweden , Designing Of LC Filter For AC Motor Drive , UPE Inc. IEEE-1995 pp(1050-

   0.4 0.405 0.41 0.415 0.42 0.425 0.43 0.435

   Time (s)

   0.4 0.405 0.41 0.415 0.42 0.425 0.43 0.435

   Time (s)

   1052)

   Mag (% of Fundamental)

   100

   80

   60

   40

   20

   Fundamental (50Hz) = 573.8 , THD= 44.63%

   Mag (% of Fundamental)

   100

   80

   60

   40

   20

   Fundamental (50Hz) = 567.4 , THD= 4.71%

4. S. Ekram,Dr. B. Sarkar , Effects of harmonics on PWM inverter fed induction machines, Vol 85 , June 2004.

5. Fang Z. Peng, Gui-Jia Su & George Farquharson, A Series LC Filter for Harmonic Compensation of AC Drives , 1999 IEEE pp(213-218)

6. Najwa Mahamad, C. M. Hadzer and Syafrudin Masri, Application of LC Filter in Harmonics Reduction, National Power & Energy

   0

   0 10 20 30 40 50

   Harmonic order

   0

   0 10 20 30 40 50

   Harmonic order

   Conference (PECon) IEEE 2004

7. Kenji Amei Masaaki Sakui Hiroshi Fuji.ta, Characteristics of a

   (a)Without filter (b)with LC filter

   Novel PWM Inverter Circuit .with a L-C Filter Connected with DC Link Toyama University IEEE PCC-Nagaoka 1997 pp759-764.

8. J. C. Balda D. C. Griffitki A. McEachern, Effects of Harmonics on Equipment Report of the IEEE Task Force on the Effects of