Abstract:
A three-phase AC voltage regulator is for adjusting a line voltage on transmission lines. The three-phase AC voltage regulator includes a sampling circuit, a reference-voltage circuit, a comparator, a switch, a power supply, and a compensator. The sampling circuit is for sampling the line voltage. The reference-voltage circuit is for receiving a line-to-line voltage from the transmission lines and generating a standard voltage. The comparator is for comparing the line voltage and the standard voltage to obtain a signal. The switch is for being turned on or off based on the signal. The power supply is for supplying various electric powers to the compensator. The compensator is for receiving the electric power and generating compensating voltages. The compensating voltages are used to compensate the line voltage.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to three-phase alternating current voltage regulators for balancing voltages on transmission lines between three-phase generators and loads, and more particularly to an automatically controlled three-phase alternating current voltage regulator. 
         [0003]    2. Description of Related Art 
         [0004]    Alternating current (AC) voltages generated from a three-phase generator are transmitted on transmission lines to various loads, such as electric motors. However, climatic conditions may result in fluctuation of the voltages in the transmission lines. If the loads receive the unstable voltages, they will operate unsteadily. Thus, it is necessary to balance the AC voltages in the transmission lines. 
         [0005]    A microcomputer is typically used in a generator. Referring to  FIG. 5 , transmission lines  10  transmitting the alternating voltage generated from a three-phase generator  80  to a load  90  is depicted. A three-phase AC voltage regulator  999  is used for balancing the voltages in the transmission lines  10 . The three-phase AC voltage regulator  999  includes a sampling circuit  20 , a reference-voltage circuit  30 , a microcomputer  40 , an interface  50 , and a compensator  70 . 
         [0006]    A line voltage is sampled from the transmission lines  10  by the sampling circuit  20 . A line-to-line voltage is received from the transmission lines  10 , and converted to a standard voltage by the reference-voltage circuit  30 . The line voltage and the standard voltage are received, and compared by the microcomputer  40  to obtain a signal. The line voltage in the transmission lines  10  is compensated with the signal by the compensator  70 . The microcomputer  40  is connected with a desktop computer via the interface  50  to monitor the three-phase AC voltage regulator  999 . 
         [0007]    However, the microcomputer is expensive, making the regulator also expensive. 
         [0008]    Therefore, a three-phase AC voltage regulator is needed in the industry to address the aforementioned deficiency. 
       SUMMARY OF THE INVENTION 
       [0009]    A three-phase AC voltage regulator is for adjusting a line voltage on transmission lines. The three-phase AC voltage regulator includes a sampling circuit, a reference-voltage circuit, a comparator, a switch, a power supply, and a compensator. The sampling circuit is for sampling the line voltage. The reference-voltage circuit is for receiving a line-to-line voltage from the transmission lines. The comparator is for comparing the line voltage and the standard voltage to obtain a signal. The switch is for being turned on or turned off based on the signal. The power supply is for supplying various electric powers to the compensator. The compensator is for receiving the electric power and generating compensating voltages. The compensating voltages are used to compensate the line voltage. 
         [0010]    Other systems, methods, features, and advantages of the present three-phase AC voltage regulator will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present device, and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Many aspects of the present three-phase AC voltage regulator can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present device. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0012]      FIG. 1  is a block diagram showing a three-phase AC voltage regulator in accordance with an exemplary embodiment, the three-phase regulator including a sampling circuit, a reference-voltage circuit, a comparator, a switch, and a compensator. 
           [0013]      FIG. 2  is a schematic diagram showing a concrete structure of the sampling circuit, and the reference-voltage circuit of  FIG. 1 . 
           [0014]      FIG. 3  is a schematic diagram showing a concrete structure of the comparator, and the switch of  FIG. 1 . 
           [0015]      FIG. 4  is a schematic diagram showing a concrete structure of the compensator of  FIG. 1 . 
           [0016]      FIG. 5  is a block diagram showing a conventional three-phase AC voltage regulator. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Reference will now be made to the drawings to describe a preferred embodiment of the present three-phase AC voltage regulator. 
         [0018]    Referring to  FIG. 1 , a three-phase AC voltage regulator  888  in accordance with a preferred exemplary embodiment is used for balancing voltage on transmission lines  100  that connects a three-phase generator  800  and a load  900 . The three-phase AC voltage regulator  888  includes a sampling circuit  200 , a reference-voltage circuit  300 , a comparator  400 , a switch  500 , a power supply  600 , and a compensator  700 . 
         [0019]    The sampling circuit  200  is used for sampling a line voltage from the transmission lines  100 . The reference-voltage circuit  300  is for receiving a line-to-line voltage from the transmission lines  100 , and converting the line-to-line voltage to a standard voltage. The comparator  400  is used for comparing the line voltage and the standard voltage to obtain a signal. The power supply  600  is used for supplying an electric power to the compensator  700 . The compensator  700  is used for receiving the electric power, and generating compensating voltage to be used to compensate the line voltage in the transmission lines  1   00 . The switch  500  is used for switching the electric power to the compensator  700  according to the signal. 
         [0020]    Referring also to  FIG. 2 , the transmission lines  100  includes three live wires  102 ,  104 ,  106 . An end of each of the live wires  102 ,  104 ,  106  is connected between a U-phase terminal, a V-Phase terminal, and a W-phase terminal of a three phrase generator respectively. Another end of each of the live wires  102 ,  104 ,  106  is connected to a U-phase terminal, a V-Phase terminal, and a W-phase terminal of a three phrase load respectively. 
         [0021]    The sampling circuit  200  includes a first sampling module  220 , a second sampling module  240 , and a third sampling module  260 . An end of each of the first sampling module  220 , the second sampling module  240 , and the third sampling module  260  is connected to the live wires  102 ,  104 ,  106  respectively. Another end of each of the first sampling module  220 , the second sampling module  240 , and the third sampling module  260  is connected to ground. The first sampling module  220  includes a transformer T 1 , a rectifier D 1 , and a filter C 1 . The second sampling module  240  includes a transformer T 2 , a rectifier D 2 , and a filter C 2 . The third sampling module  260  includes a transformer T 3 , a rectifier D 3 , and a filter C 3 . The three sampling modules  220 ,  240 ,  260  have similar structures and functions. Hereinafter, the first sampling module  220  is depicted as an example representing the three sampling modules  220 ,  240 ,  260 . 
         [0022]    An end of a primary coil  221  of the transformer T 1  is electrically connected to the live wire  102 , and another end of the primary coil  221  is connected to ground. The transformer T 1  is used to sample the line voltage of the live wire  102 . Two ends of the secondary coil  222  are respectively coupled to two input terminals  223 ,  224  of the rectifier D 1 . A ground terminal  225  of the rectifier D 1  is connected to ground, and an output terminal  226  of the rectifier D 1  is electrically connected to a first terminal  202 . An end of the filter C 1  is connected to ground, and another end of the filter C 1  is electrically connected to the first terminal  202 . Similarly, the second sampling module  240  includes a second terminal  204  and the third sampling module  260  includes a third terminal  206 . 
         [0023]    When the first sampling module  220  operates, the primary coil  221  samples the line voltage U A  and the secondary coil  222  generates a first induced voltage U 1  according to the line voltage U A . The first induced voltage U 1  is then rectified by the rectifier D 1  and filtered by the filter C 1  before yielding a first sampled voltage. The first sampled voltage is generated from the first terminal  202 . 
         [0024]    The reference-voltage circuit  300  includes a transformer T 4 , a rectifier D 4 , and a filter C 4 . Two ends of a primary coil of the transformer T 4  are correspondingly connected to the live wire  104 ,  106 . Two ends of a secondary coil of the transformer T 4  are correspondingly connected to two input terminals of the rectifier D 4 . A ground terminal of the rectifier D 4  is connected to ground, and an output terminal of the rectifier D 4  is electrically connected to a fourth terminal  302 . An end of the filter C 4  is connected to ground, and another end of the filter C 4  is also connected to the fourth terminal  302 . 
         [0025]    When the reference-voltage circuit  300  operates, the transformer T 4  receives the line-to-line voltage between the live wire  104  and the live wire  106  and generates a second induced voltage. The second induced voltage is then rectified by the rectifier D 4  and filtered by the filter C 4  before yielding the standard voltage. The first sampled voltage is generated from the fourth terminal  302 . 
         [0026]    Referring to  FIG. 3 , the comparator  400  includes a first comparing module  410 , a second comparing module  420 , and a third comparing module  430 . The first comparing module  410  is electrically connected to the first terminal  202 , the fourth terminal  302 , and the switch  500 . The second comparing module  420  is electrically connected to the second terminal  204 , the fourth terminal  302 , and the switch  500 . The second comparing module  430  is electrically connected to the third terminal  206 , the fourth terminal  302 , and the switch  500 . The three comparing modules  410 ,  420 ,  430  have similar structures and functions. Hereinafter, the first comparing module  410  is depicted as an example representing the three comparing modules  410 ,  420 , and  430 . 
         [0027]    The first comparing module  410  includes a first comparing unit  412 , a second comparing unit  414 , a first time-delay unit  416 , and a second time-delay unit  418 . The first comparing unit  412  and the second comparing unit  414  are used for comparing the first sampled voltage with the standard voltage. If the first sampled voltage is greater than the standard voltage, the first comparing unit  412  generates a first output voltage, otherwise the second comparing unit  414  generates a second output voltage. The first time-delay unit  416  is for delaying the first output voltage and the second time-delay  418  is for delaying the second output voltage. 
         [0028]    The first comparing unit  412  includes an operational amplifier (op-amp) A 1 . A noninverting input of the op-amp A 1  is connected to the first terminal  202  via a resistor, an inverting input is connected to the fourth terminal  302  via two serial resistors, and an output is connected to the first time-delay unit  416 . 
         [0029]    The first time-delay unit  416  includes a first RC (Resistor and Capacitor) network and a bipolar junction transistor (BJT) Q 1 . An end of the first RC network is connected to the output of the op-amp A 1 , and another end of the RC network is connected to a base of the BJT Q 1 . An emitter of the BJT Q 1  is connected to ground, and a collector of the BJT Q 1  is connected to the switch  500 . 
         [0030]    The op-amp A 1  is for comparing the first sampled voltage with the standard voltage. The first RC network and the BJT Q 1  are used to delay the first output voltage. The first RC network includes four capacitors and three resistors. The three resistors are serially connected between the op-amp A 1  and the BJT Q 1 . There are four interconnections among the op-amp A 1 , the BJT Q 1 , and the three resistors. Each interconnection is connected to ground via one of the four capacitors respectively. 
         [0031]    When the first RC network receives the first output voltage, four parallel connected capacitors charge in turn to delay the first output voltage. When the base of the BJT Q 1  receives the first output voltage, the BJT Q 1  turns on and allows the switch  500  operate. 
         [0032]    The second comparing unit  414  includes op-amps A 2 , and A 3 . A noninverting input of the op-amp A 2  is connected to the fourth terminal  302  via a resistor, and an inverting input of the op-amp A 2  is connected to the first terminal  202 , and an output is connected to a noninverting input of the op-amp A 3  via a resistor. An inverting input of the op-amp A 3  is connected to the fourth terminal  302 . An output of the op-amp A 3  is connected to the second time-delay unit  418 . 
         [0033]    The second time-delay unit  418  includes a second RC network and a BJT Q 2 . One end of the second RC network is connected to the output of the op-amp A 3 , and another end of the RC network is connected to a base of the BJT Q 2 . An emitter of the BJT Q 2  is connected to ground, and a collector of the BJT Q 2  is connected to the switch  500 . 
         [0034]    The op-amps A 2 , and A 3  are for comparing the first sampled voltage with the standard voltage. The second RC network and the BJT Q 2  are combined to delay the first output voltage. The second RC network includes three capacitors and two resistors. The two resistors are serially connected between the op-amp A 1  and the BJT Q 1 . There are three interconnections among the op-amp A 1 , the BJT Q 1 , and the two resistors. Each interconnection is connected to ground via one of the three capacitors respectively. 
         [0035]    When the second RC network receives the second output voltage, three parallel connected capacitors charge in turn to delay the second output voltage. When the base of the BJT Q 2  receives the second output voltage, the BJT Q 2  is enabled and actuates the switch  500 . 
         [0036]    The switch  500  is connected to a fifth terminal  602  of the power supply  600  to receive a positive voltage, and connected to a sixth terminal  604  of the power supply  600  to receive a negative voltage. The switch  500  includes three switching modules  510 ,  520 ,  530 . The switching module  510  is connected to the first comparing module  410 , the fifth terminal  602 , and the sixth terminal  604 . The switching module  510  includes a seventh terminal  502 . The switching module  520  is connected to the second comparing module  420 , the fifth terminal  602 , and the sixth terminal  604 . The switching module  520  includes an eighth terminal  504 . The switching module  530  is connected to the third comparing module  430 , the fifth terminal  602 , and the sixth terminal  604 . The switching module  530  includes a ninth terminal  506 . Hereinafter, the switching module  510  is depicted as an example representing three switching modules  510 ,  520 ,  530 . 
         [0037]    The switching module  510  includes a first relay  512  and a second relay  514 . The first relay  512  is connected to the collector of the BJT Q 1  of the first time-delay unit  416 , the fifth terminal  602 , and the seventh terminal  502 . The second relay  514  is connected to the collector of the BJT Q 2  of the second time-delay unit  418 , the sixth terminal  604  and the seventh terminal  502 . 
         [0038]    When the BJT Q 1  is enabled, the first relay  512  leads the positive voltage from the fifth terminal  602  to the seventh terminal  502 . When the BJT Q 2  is enabled, the second relay  514  leads the negative voltage from the sixth terminal  604  to the seventh terminal  502 . 
         [0039]    Referring to  FIG. 4 , the compensator  700  includes three compensating modules  710 ,  720 ,  730 . The compensating module  710  is connected to the transmission lines  100  and a seventh terminal  502 . The compensating module  710  includes a transformer T 5 , an adjustable transformer T 8 , and a motor M-A. The compensating module  720  is connected to the transmission lines  100  and an eighth terminal  504 . The compensating module  720  includes a transformer T 6 , an adjustable transformer T 9 , and a motor M-B. The compensating module  730  is connected to the transmission lines  100 , and an ninth terminal  506 . The compensating module  730  includes a transformer T 7 , an adjustable transformer T 10 , and a motor M-C. The three compensating modules  710 ,  720 ,  730  have similar structures and functions. Hereinafter, the compensating module  710  is depicted as an example representing three compensating modules  710 ,  720 ,  730 . 
         [0040]    Two ends of a primary coil  711  of the transformer T 5  are correspondingly connected to two slidable contacts  713 ,  714  of the adjustable transformer T 8 . The slidable contacts  713 ,  714  are also connected to the motor M-A. A secondary coil  712  of the transformer T 5  is connected to the live wire  102 . The motor M-A is connected to the seventh terminal  502 . A end of the adjustable transformer T 8  is connected to the live wire  102 , and the other end is connected to ground. 
         [0041]    When the adjustable transformer T 8  and the transformer T 5  operate, the secondary coil  712  generates an induced voltage U 5 . The induced voltage U 5  is fed back to the line voltage U A . The motor M-A receives the positive voltage or the negative voltage from the seventh terminal  502 , to rotate in a positive direction or a negative direction directly. Therefore, the slidable contacts  713 , and  714  are moved by the motor M-A to further adjust the adjustable transformer T 8 . 
         [0042]    The comparator  400  and the switch  500  are used in the three-phase AC voltage regulator  888  to control the compensator  700 . Herein, the comparator  400  and the switch  500  are composed of ordinary electronic components, such as op-amp, BJT, resistor, and capacitor. Therefore, the three-phase AC voltage regulator  888  is cheaper. 
         [0043]    It should be emphasized that the above-described preferred embodiment, is merely a possible example of implementation of the principles of the invention, and is merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and be protected by the following claims.