Abstract:
The present invention relates to a device for power factor correction and electrical wide band filtering in electrical systems for reducing considerably voltages of frequencies higher than 110 Hz on power systems rated for 10 Hz to 60 Hz and to improve power factor by injecting reactive power into the system. The device of the present invention provides a combination of inductors and capacitors which effectively corrects the power factor and filters out voltages of high frequencies.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a device for power factor correction and electrical wide band filtering in electrical systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    Filtering out undesired harmonic frequencies and reducing high frequency voltages from the current in power systems is advantageous in order to reduce damage or improper operation of electrical equipment connected to the power system. In closed electrical systems, such as on board fishing ships, such disturbances cause increased use of oil to produce the desired amount of energy, which is followed by heat generation in all the electricity system and wear on the system it self and the electrical equipment connected to the system. 
         [0003]    U.S. Pat. No. 3,555,291 discloses a harmonic filter for an AC power system, designed for converter installations, having of a plurality of conventional LC shunt filters tuned to the expected harmonic frequencies. U.S. Pat. No. 3,555,291 uses damping to diminish the effects of parallel resonance and this system can also contain static capacitors for power factor correction. This system further comprises an additional filter, being a LC filter with a resistor connected in parallel with the inductance, which is tuned to provide damping at the harmonic frequency at which parallel resonance may occur. The resistor in this setup provides damping and therefore reducing the amplitude of oscillations under parallel resonant conditions. 
       SUMMARY OF THE INVENTION 
       [0004]    It is an object of the present invention to provide an improved device and method. 
         [0005]    The object of the invention is achieved by the features of the claims and/or the following aspects of the present invention. 
         [0006]    In particular, it is a preferred advantage of the present invention to provide a device for reducing considerably voltages and current of frequencies higher than 110 Hz on power systems rated for 10 Hz to 60 Hz and/or to improve power factor. 
         [0007]    In particular, the electric correction unit and the method for reducing voltages and current of undesired frequencies of the present invention improves power factor by injecting reactive power into the system. A preferred embodiment of the device (in the following also labelled as electric correction unit) of the present invention provides a combination of inductors and capacitors in such a manner that a low pass filter is connected in series with a band-stop filter unit, which also acts as power factor correction unit, an the electric correction unit is connected to the system in parallel to the load. 
         [0008]    The electric correction unit reduces voltages of undesired frequencies carried on the carrier frequency and thereby reduces heat-formation in the power system. As the band-stop filter unit is serially connected behind/after the low pass filter, the high frequencies are drawn into the low pass filter and eliminated there, whereas the distortion in the lower frequency range is corrected or eliminated in the band-stop filter unit. The band-stop filter unit draws fifth harmonic frequencies towards it and the voltages of undesired frequencies are carried on the fifth harmonic. As the band-stop filter unit is serially connected behind/after the low pass filter, the high frequencies are pulled into the low pass filter and eliminated there. The band-stop filter unit of the present invention is designed such that the capacitors are connected in a delta connection and inductor units (reactors) are connected in a star (Y or Wye) connection. 
         [0009]    The band-stop filter unit is preferably loaded with the tuned frequency (frequencies) that shall be reduced, e.g. 250 Hz on a system rated 50 Hz. In this case the 250 Hz current is a carrier for voltages of higher frequencies, e.g., from 10 3  Hz to 10 10  Hz that are preferably considerably reduced in the low pass filter. 
         [0010]    In a first aspect of the present invention an electric correction unit is provided for an electrical system. The electric correction unit comprises a low pass filter and a band-stop filter unit, where the band-stop filter unit is serially connected to the low pass filter and the electric correction unit is connected in parallel with load on the system. 
         [0011]    In a second aspect of the present invention a method is provided for reducing voltages of undesired frequencies and improving power factor in power systems, the method comprising placing an electric correction unit adjacent to a major load in the system, the electric correction unit comprises a low pass filter and a band-stop filter unit. The band-stop filter unit is serially connected to the low pass filter and the unit is connected in parallel with load on the system. 
         [0012]    The operating frequency of combined filter is preferably 110 Hz to 10 10  Hz, preferably from 110 to 10 9  Hz, or from 250 to 10 8  Hz, or from 110 to 10 8  Hz, or from 250 to 10 9  Hz, or from 110 to 10 7  Hz, where the operating frequency of the reactive power unit preferably ranges from 10 Hz to 400 Hz, depending on the rated frequency of the power system. 
         [0013]    In an embodiment of the present invention the electric correction unit, which may also acts as band-stop filter unit is detuned closed to the frequencies that shall be eliminated, e.g. close to 250 Hz in case of 5 th  harmonic (for a system rated 50 Hz). 
         [0014]    In an embodiment of the present invention the operating frequency of the low pass filter assembly is preferably from 10 3  to 10 1 ° Hz, preferably from 10 4  to 10 9  Hz, or from 10 4  to 10 8  Hz, or from 10 3  to 10 8  Hz, or from 10 4  to 10 9  Hz, or from 10 3  to 10 7  Hz. 
         [0015]    In an embodiment of the present invention the operating frequency of the band-stop filter unit is preferably from Hz from 110 to 910 Hz, or from 110 to 810 Hz, or from 110 to 740, or from 310 to 710 Hz, from 410 to 610 Hz. or from 110 to 310 Hz. 
         [0016]    In a specific embodiment of the present invention the operating frequency of the one or more band-stop filter unit is that it passes through frequencies in the range from 180 to 290 Hz, such as 180 to 240 Hz for a system with operating frequency of 50 Hz and preferably 210 Hz or 230 to 290 Hz for a system with operating frequency of 60 Hz and preferably 260 Hz. 
         [0017]    In a specific embodiment of the present invention the electric correction unit is operating in a 10 to 800 Hz power system, such as in a 10 to 400 Hz power system, or 10 to 200 Hz power system, or 10 to 60 Hz power system, such as 50 Hz power system or a 60 Hz power system. 
         [0018]    In an embodiment of the present invention the rated voltage can range from 100 V to 750 kV and the rated current can range from 1 A to 100 kA. 
         [0019]    In a specific embodiment of the present invention the low pass filter used in the assembly of the electric correction unit is a 3-line EMC filter of the series B84143B* S020 . . . . S024 obtainable from EPCOS AG. 
         [0020]    In an embodiment of the present invention the electric correction unit relates to a device for conditioning the power system. In the present context the term “conditioning” refers to filtering out voltages of undesired frequencies, improving the power factor or correcting the power factor in the system. 
         [0021]    In an embodiment of the present invention the electric correction unit is installed in a closed electrical system such as a fishing vessel. Devices such as winches for pulling fishing nets use an enormous amount of electricity and therefore increase the use of oil, which is used for generating electricity for the vessel. When winces and other electricity demanding devices are in use, disturbances in the form of low and high frequency voltages are being generated in the system. The electric correction unit is installed close to an electricity demanding device, such as a winch, in order to prevent distribution of reducing voltages and current of undesired frequencies throughout the system. 
         [0022]    In the present context the term “low pass filter” or “low pass filter unit” refers to a filter that passes low-frequency signals but attenuates, or reduces the amplitude of signals with frequencies within the bandwidth of the filter (but attenuates, or reduces the amplitude of signals with frequencies) being higher than the cut-off frequency for said filter. The actual amount of attenuation for each frequency varies from filter to filter. Furthermore, a low-pass filter assembly refers to a plurality of low-pass filters, which are identical, i.e. having the same bandwidth and same lower and upper cut-off frequencies. 
         [0023]    In the present context the term “band-stop filter unit” refers to an assembly of reactors (inductor units) and capacitors in a three-phase system (see  FIG. 3 ), where the capacitors are connected in a delta connection and inductor units (reactors) are connected in a star (Y or Wye) connection. The band-stop filter unit attenuates, or reduces the amplitude of signals with frequencies within the operating frequency of the filter. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0024]    The present invention will now be disclosed in reference to the drawings illustrating the specific embodiments of the invention. The specific embodiments disclosed herein should not be limiting to the invention as described in the claims and the description. 
           [0025]      FIG. 1  is a schematic diagram of a power system according to an embodiment of the present invention where the electrical correction unit is connected in parallel with load on the system. 
           [0026]      FIG. 2  is a schematic drawing of a prior art low pass filter used in the device of the present invention. 
           [0027]      FIG. 3  is a schematic drawing of band-stop filter unit according to one embodiment the present invention. 
           [0028]      FIG. 4  is a schematic drawing of the electrical correction unit of the present invention 
           [0029]      FIG. 5  shows the current load, under variable load condition, with and without the correction unit. 
           [0030]      FIG. 6  shows actual power, under variable load condition, with and without the correction unit. 
           [0031]      FIG. 7  shows the voltage, under variable load condition, with and without the correction unit. 
           [0032]      FIG. 8  shows current disturbance in percentage, under variable load condition, with and without the correction unit. 
           [0033]      FIG. 9  shows voltage disturbance in percentage, under variable load condition, with and without the correction unit. 
           [0034]      FIG. 10  shows current, power, and frequency disturbance, under normal load condition, with and without the correction unit. 
           [0035]      FIG. 11  shows kvar, kVA, and the percentage of disturbance of kVA and frequency, under normal load condition, with and without the correction unit. 
           [0036]      FIG. 12  shows percentage of disturbance of, under normal load condition, with and without correction unit. 
           [0037]      FIG. 13  shows percentage of disturbance of, under normal load condition, with and without correction unit. 
           [0038]      FIG. 14  shows system frequency, and WW, under normal load condition, with and without correction unit. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0039]      FIG. 1  shows a schematic diagram of a power system  1  in a ship having a generator  2 , which generates voltages at a 50 Hz or 60 Hz frequency for winches  4 , and other devices  5 ,  6 , and  12  which depend on electricity. The system shown in  FIG. 1  also comprises an AC/DC converter  7 . The electrical correction unit  8  comprises a low pass filter assembly  9  and a band-stop filter unit  10 . The low pass filter  9  is connected in parallel to the load as shown in  FIG. 1 . The band-stop filter unit  10  that also acts as power factor correction unit, is connected in series with the low pass filter  9 . 
         [0040]      FIG. 2  is a schematic drawing of one of many suitable commercially of the shelf available high frequency EMC filter units. A suitable EMC filter unit from EPCOS© was select for the particular system setup and test will be elaborated on in this section. Other test systems with different configuration have also been tested. 
         [0041]      FIG. 3  is a schematic drawing of band-stop filter unit according to an embodiment of the present invention with a capacitor connected behind each inductor unit. The band-stop filter unit is designed with the tuned frequency (frequencies) that shall be reduced, e.g. 250 Hz on a system rated 50 Hz. In this case the 250 Hz is the carrier frequency for voltages of higher frequencies, from 10 3  Hz to 10 10  Hz that are considerably reduced in the low pass filter. As can be seen in  FIG. 3  the capacitors are connected in a delta connection and inductor units (reactors) are connected in a star connection. The calculation for the size of the reactor units depends on the frequency and the voltage of the system. 
         [0042]      FIG. 4  is a schematic drawing of an electrical correction unit according to a preferred embodiment having three low pass filter units ( 9 ( 1 ),  9 ( 2 ),  9 ( 3 ) and six band-stop filter units ( 10 ( 1 )- 10 ( 6 ). The third set of low pass filter unit  9 ( 3 ) and band-stop filter units ( 10 ( 5 )- 10 ( 6 ) are shown as broken lines as an alternative embodiment. Each low pass filter unit and band-stop filter unit are connected to all lines in the three-phase electrical system (L 1 -L 3 ) as shown in  FIGS. 2 and 3 . Under different conditions where based on the load on the system one or more low pass filter units  9  are switched on as well as two band-stop filter units  10 . A computer is connected to all the units and switches on the additional band-stop filter units when the load on the system increases. 
         [0043]    In the following examples, variable high load situations will now be discussed with reference to  FIGS. 5-9 . Generally, when the winches haul in the fishing gear, the generator load varies considerably. One of the reasons for this is the vertical motion of the ship, caused by rough seas. The performance of the electrical correction unit was tested in these conditions, as is shown in the following text. The first half of each plot in  FIGS. 5-9  demonstrates the electrical system operation when the electrical correction unit is switched ON and the second half of the plot with the correction unit switched OFF. 
         [0044]    The system phase current is shown in  FIG. 5  and the power load in  FIG. 6 . In the first half, when the correction unit is ON, it can be seen that the ampere load fluctuates at about 400 A and in accordance with the power load. In the second half, the current rises to about 700 A and is not in accordance with the power load. This stems from the fact that the generator is hyper magnetized and the voltage regulator is not functioning properly because of high frequency interference, as shown in  FIG. 7 . 
         [0045]      FIG. 8  shows the Total Harmonic Distortion (THD) of the current sinusoidal wave form. When the correction unit is switched ON, the THD level of the current wave form ranges between 15-25% and varies in accordance with the ampere load of  FIG. 5 . Once the correction unit is switched OFF, the THD level of the wave form rises to about 30% and fluctuates slightly, because of limited fluctuation in the ampere load. 
         [0046]      FIG. 9  shows the THD of the voltage sinusoidal wave form. Again, when the correction unit is switched ON, the THD level of the curve is relatively small, i.e. around 6-7%, and varies in accordance with the voltage of  FIG. 7 . When the correction unit is switched OFF the THD of the voltage wave form rises to approximately 13%. 
         [0047]    Similarly,  FIGS. 10-14  show the system of the same fishing vessel under low load with and without the electrical correction unit switched ON. In all the figures the horizontal axis shows time in 10 minute intervals. In  FIG. 10  the vertical axis shows the current [A], the active power [KW] and power factor. During the first 20 minutes the electrical correction unit is ON. The current is quite stable around 110 A as is the power load of 57 KW. The power factor is also fairly good, around 0.75. Then, when the electrical correction unit is switched OFF at 7:38, the system enters an unbalanced state with a lot of interference and the power factor goes down to 0.3, which is far too low.  FIG. 11  shows reactive power, apparent power, phase current symmetry and phase voltage symmetry. The plot shows how the correction unit reduces reactive power and stabilizes the system. 
         [0048]      FIG. 12  shows the THD percentage level of the phase currents during the same period. With the correction unit ON, the THD in each phase current is approximately 5%, while it rises to 14-16% with the correction unit switched OFF. 
         [0049]      FIG. 13  similarly shows the THD percentage level of the phase voltage. With the correction unit on the THD level is approximately 4% and without the correction unit it is approximately 10%. 
         [0050]    The electrical system frequency is the first plot of  FIG. 14 . The frequency is clearly very stable at 50.5 Hz with the correction unit switched ON. Once the correction unit is switched OFF the frequency starts fluctuating. The two other plots show the active power in 5 th  and the 11 th  Harmonic Frequency. Attention should be drawn to the fact that when the correction unit is switched ON, almost no power is in harmonic frequencies, but when the unit is switched OFF; power is clearly detected in these harmonic frequencies. 
         [0051]    High frequency distortion in electrical systems is largely caused by AC/DC converters and many other devices. The most common solution to eliminate these high frequency distortions is to filter them out and convert them to heat. The uniqueness of the design of the electrical correction unit is not to convert these distortions to heat but to remove them through a process of elimination. 
         [0052]    One of the main advantages of the electrical correction unit is that it significantly corrects the Power Factor (PF) of the electrical system. By correcting the PF, the phase lag between voltage and current is eliminated. This will be demonstrated in Table 1, here below, and it can also be seen in  FIG. 10 . The table reflects the same power reading, when the correction unit is switched OFF, but the current rises significantly from 270 A to 640 A and the PF drops from about 0.87 to 0.35. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Electrical 
                 Electrical 
               
               
                   
                 Correction Unit 
                 Correction Unit 
               
               
                   
                 On 
                 Off 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Generator 
                 35-45° C. 
                 60-80° C. 
               
               
                   
                 Temperature 
               
               
                   
                 Real Power 
                 160 KW 
                 160 KW 
               
               
                   
                 Current 
                 270 A 
                 640 A 
               
               
                   
                 Power Factor 
                 0.85-0.9 
                 0.3-0.4 
               
               
                   
                 Reactive Power 
                 90 KVAr 
                 380 KVAr 
               
               
                   
                 Apparent Power 
                 190 KVA 
                 410 KVA 
               
               
                   
                   
               
             
          
         
       
     
         [0053]    By correcting the PF, eliminating high frequency and harmonic distortions, the electrical correction unit significantly reduces the generator load and thus saves a lot of energy. This can be seen in Table 1, when the correction unit reduces the apparent power by 220 KVA (54%) and the generator temperature drops by 30° C. (57%). 
         [0054]    In an example of the function and the generation of the device of the present invention, for the disclosed electric correction unit is in an electrical system distant from the main power grid. The example shows the calculation of component values of a specific system. This is a 400V, 50 Hz system with an output of 217.5 A. 
         [0055]    Instead of the electrical shocks of a local system distant from the main grid forcing the main system into some imbalanced state, the distortion of the local system is injected into the local system and the main frequency of the system becomes the carrier frequency of the distortion. Experiments of the inventors have shown that due to high impedance on the grid, load on the system, distant from the local load can cause similar effects as in a smaller system such as in a ship. This of course can be calculated for each system as shown here below by a calculation of the components values used in the band-stop filter unit of the present invention. The unit both corrects the phase shift between the voltage potential in each phase of the system and the current. This indeed is revolutionary for the current practice. 
         [0056]    Requirements for the band-stop filter unit: 
         [0057]    Connection of capacitor in a delta connection and inductor unit (reactor) in a star connection. 
         [0000]                                                        Size of capacitor     996 micro F   Frequency   50 Hz           Size of reactor   0.136 mH   Voltage   400                        
On 50 Hz: Xc=3,198 ohm (in a delta-connection)
       Xl=0.043 ohm (in a star-connection)       
 
         [0059]    Capacitor recalculated for star-connection—By using 3 capacitors (MKK400-d-50-21 (3×332 micro F) in each system (smt.4 system) 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 On 50 Hz: 
                 Xc = 1.066 ohm 
                   
               
               
                   
                   
                 Xl = 0.043 ohm 
               
               
                   
                   
                 Ztot = 1.023 ohm 
                 3-phase power: 150.5 kVAr 
               
               
                   
                   
                   
                 Phase current: 217.5 A 
               
               
                   
                   
               
               
                   
                 Size of capacitor 2988 micro F 
               
               
                   
                 Size of reactor 0.136 mH 
               
             
          
         
       
     
         [0060]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and non-restrictive; the invention is thus not limited to the disclosed embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be considered as limiting the scope.