Abstract:
A terminal voltage equalization circuit is used to equalize the terminal voltage of the series of connected battery strings so that each battery in the series of connected battery strings can be equally charged. When voltage of a certain battery in the battery string is higher than that of the other batteries, the battery voltage sensing and controlling circuit will output a high frequency signal to drive the switch devices to transit power from the high voltage batteries to the low voltage batteries by transformer. By the high switching switches, the charging currents through the batteries with high terminal voltages can be reduced, the charging currents through the batteries with low terminal voltages can be enhanced, and therefore the damages to the batteries due to overcharging can be avoided and speedy balance of the terminal voltages between each battery can be achieved.

Description:
BACKGROUND OF THE PRESENT INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention generally relates to an energy equalization circuit for a battery charger, and more particularly to an equalization circuit for balancing the terminal voltages of each battery.  
         [0003]     2. Description of the Prior Art  
         [0004]     It is often needed to cascade many batteries in a series of connected battery strings in practice, for example, the electric motorcycle needs four Lead-Acid batteries and the electric bicycle needs two or three Lead-Acid batteries to compose a series of connected battery strings, therefore whether the state of charge, capacity, and characteristic of each battery match for each other is extraordinarily important in the series of connected battery strings. Besides, since the state of charge of each battery in the series of connected battery strings varies as the using times increase and according to whether it matches for other batteries in the series of connected battery strings, and the state of charge of the batteries in the series of connected battery strings is hard to measure, therefore the difference between the terminal voltages of each battery in the battery strings increases and the batteries with higher level/amount of state of charge are more easily damaged due to being overcharged. Hence, each battery in the series of batteries can operate under the best conditions by appropriately sensing and adjusting the situation of a single battery, for example, balancing the terminal voltages between each battery in the series of connected battery strings when there is difference between the terminal voltages of each battery, and thus extending the life of the batteries, which is the main purpose of the equalizer.  
         [0005]      FIG. 1  represents a conventional dissipative type equalizer constituted with resistors, wherein the series of connected battery strings is connected by three batteries B 1 , B 2  and B 3 ; and I represents a direct current source used to charge the series of batteries. Referring to  FIG. 1 , batteries B 1 , B 2  and B 3  are respectively connected with the by-pass circuits which are constituted by resistors R 1 , R 2 , R 3  and switches S 1 , S 2 , S 3 . Furthermore, a battery voltage sensing and controlling circuit is used to control the operation of the equalizer. The battery voltage sensing and controlling circuit senses and controls the terminal voltages between batteries B 1 , B 2 , and B 3  continuously while the battery string is being charged. Under the general principles, it is assumed that the battery B 1  exceeds the battery B 2  and B 3  in terminal voltages. When the terminal voltage of battery B 1  is detected to be higher than that of batteries B 2  and B 3  and over a predestinate value, the battery voltage sensing and controlling circuit will output a signal from P 1  to turn on the switch device S 1 . At this time, the battery B 1  and resistor R 1  are in parallel connecting and let a part of charging current pass through the resistor R 1  and reduce the current flowing through the Battery B 1  (I B1 =I− R1 ) Besides, the current flowing through the batteries B 2  and B 3  is still I. Hence, the rising rate of terminal voltage of battery B 1  can be slowed down and the terminal voltage of each battery in the battery strings can gradually achieve balance.  
         [0006]     The above-mentioned resistance type equalizer uses the shunt resistors to consume the imbalanced power between each battery in the series of connected battery strings. Therefore, more heat will be generated in the circuit and the efficiency will be lower, which shows that this type of equalizer is not economical.  
         [0007]      FIG. 2  represents a non-dissipative type equalizer constituted with the transformers. The circuit structure in  FIG. 2  is similar to that in  FIG. 1 , but three identical flyback type transformers T 1 , T 2 , T 3  are used to substitute the resistors and high frequency signal generators are added in the battery voltage sensing and controlling circuit. Furthermore, the turn numbers of the secondary windings are the same, but the polarity of the secondary winding is opposite to that of the primary winding in all transformers. When the difference of the terminal voltages between battery B 1  and batteries B 2 , B 3  reaches a predetermined value, the battery voltage sensing and controlling circuit will output a high frequency signal from P 1  to drive switch device S 1  and then turn on and off continuously to let the primary winding of transformer T 1  transfer energy to the secondary winding. The induced current then goes back to charging loop through the diode D 1  to charge the series of battery strings. Thus, the rising rate of the terminal voltage of battery B 1  can be slowed down and a balance between each battery of the battery strings can be gradually achieved, and the imbalanced power in battery B 1  can also be recycled for using during the equalization process.  
         [0008]     The method using the non-dissipative type transformer for equalizing potential of batteries can eliminate the problems of heat and low efficiency, etc. caused by the dissipative type resistance equalizer circuit. But a number of transformers equal to the number of batteries in the battery strings have to be used, and the volume and weight of transformers will increase the size and weight of the circuit greatly when many batteries have to be used to cascade a series of battery strings in practice.  
         [0009]     Consequently, the non-dissipative type circuit of equalizer should be improved to obtain a smaller and more flexible circuit structure for accomplishing advantages such as less heat, high efficiency, small volume and light weight.  
       SUMMARY OF THE PRESENT INVENTION  
       [0010]     The problems in the above-mentioned techniques are more heat, low efficiency, large volume and heavy weight, therefore the present invention provides an equalization circuit for series of connected battery strings to ensure the batteries in the battery strings will operate under the best conditions.  
         [0011]     Another main purpose of the present invention is to provide a forward type power transfer means for speedy equalizing effect by transferring the imbalanced energy from the batteries with high terminal voltages to the batteries with low terminal voltages directly during the process of equalization between each battery in the series of connected battery strings.  
         [0012]     Still another main purpose of the present invention is to provide an equalizer for the series of connected battery strings to reduce total volume of the transformers in the circuit effectively and to reduce the size and weight of the whole circuit substantially.  
         [0013]     The present invention includes a transformer, which is constituted by a primary winding and a secondary winding, the primary windings have the same number of windings and the identical polarity, the number of winds of the secondary winding being identical to the sum of the number of windings of the primary winding; and a switch means, which is constituted by a plurality of switch components, each of the switch component connecting with the plurality of windings in the primary winding in identical polarity, when the plurality of switch components being turned on simultaneously by a control signal, the plurality of windings in the primary winding become a primary winding and a secondary winding to each other individually. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a circuit diagram of the dissipative type equalizer of the series of connected battery strings.  
         [0015]      FIG. 2  is a circuit diagram of the non-dissipative type equalizer of the series of connected battery strings.  
         [0016]      FIG. 3  is a function block diagram of an embodiment of the present invention.  
         [0017]      FIG. 4  is a circuit diagram of an embodiment of the present invention.  
         [0018]      FIG. 5  is a circuit diagram of an embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     The following descriptions of the circuit of present invention do not include the complete structure of the equalizer. It just quotes the key points of traditional techniques to illustrate the present invention. Moreover, all of the drawings related to the present invention are not made according to the scales, and they are just used to represents the characteristics of structure of present invention.  
         [0020]     The present invention includes a transformer means, which is constituted by a primary winding and a secondary winding, the primary winding being constituted by a plurality of windings with the identical number of windings and the identical polarity, the number of windings of the secondary winding being identical to the sum of the number of windings of the primary winding; and a switch means, which is constituted by plurality of switch components, each of the switch component connecting with a plurality of windings in primary winding in identical polarity, when a plurality of switch components being turned on simultaneously by a control signal, the plurality of windings in the primary winding become a primary winding and a secondary winding to each other individually.  
         [0021]      FIG. 3  shows a function block diagram of an embodiment of the present invention. Block  301  includes a series of connected battery strings and a charge circuit. The terminal voltages of batteries in the series of connected battery strings are sensed by the battery voltage sensing and controlling circuit in block  302  via wires  311  to sense whether the difference in terminal voltages between any two batteries is normal. Block  301  will maintain the charging process when the difference in terminal voltages between any two batteries is regular. Otherwise, when the difference in terminal voltages between any two batteries is irregular, that means the terminal voltages of a certain battery in the series of connected battery strings is too high or too low, then the battery voltage sensing and controlling circuit in block  302  will output a high frequency signal via wires  312  to drive the equalization circuit in block  303 , and equalize the energy of each battery in the series of connected battery strings in block  301  via wires  313 . At the same time, block  302  is still sensing the terminal voltages of each battery in the series of connected battery strings in block  301  via wires  311 . It outputs the high frequency signal via wires  312  to drives block  303  continuously to maintain the equalization process of the terminal voltages of each battery in the series of connected battery strings when the difference in the terminal voltages between each battery is still irregular. Otherwise, the battery voltage sensing and controlling circuit in block  302  will stop outputting the high frequency signal via wires  312  for stopping the equalization process in block  301  when the difference in the terminal voltages between each battery recovers, then the circuit returns to regular charge mode.  
         [0022]      FIG. 4  is a circuit block diagram of the equalizer of an embodiment of the present invention. Block  401  is a series of connected battery strings constituted with a current source and a plurality of batteries, the current source is a direct current source I and the series of connected battery strings is composed by four series of connected batteries B 1 , B 2 , B 3  and B 4  in this embodiment. The positive terminal of current source I connects with the positive terminal of battery B 1  and the negative terminal of current source I connects with the negative terminal of battery B 4 . Block  402  is a battery voltage sensing and controlling circuit, which utilizes a micro-controller with five input ports VD 1 , VD 2 , VD 3 , VD 4 , VD 5  for sensing the terminal voltages of batteries B 1 , B 2 , B 3 , B 4  individually and four output ports TS 1 , TS 2 , TS 3 , TS 4  for outputting the driving signal to the switching components in block  403  (e.g. three terminal device such as field effect transistor) in this embodiment, wherein it has an individual driving signal or the same driving signal from output ports TS 1 , TS 2 , TS 3 , TS 4  to control switching components S 1 , S 2 , S 3 , S 4 . Block  403  is an equalization circuit constituted with a transformer T, four identical high frequency switching components S 1 , S 2 , S 3 , S 4  and five identical two terminal devices (e.g. diode or the internal parasitism diode of the field effect transistor) D 1 , D 2 , D 3 , D 4 , Dk for forming a loop. The windings N 1 , N 2 , N 3 , N 4  of the transformer T all have the same number and polarity (e.g. the dot end symbolizes positive end, the opposite end is negative end), and can become a primary or secondary winding dependent on the status of the switched component. Therefore transformer T is a forward type transformer. The number of windings of another internal winding Nk of forward type transformer can be determined by the number of batteries in the battery strings. There are four batteries with corresponding four windings N 1 , N 2 , N 3 , N 4  in this embodiment, therefore the number of winding Nk is four times of the number of winding N 1 . The polarity of winding Nk is opposite to winding N 1 .  
         [0023]     In  FIG. 4 , battery voltage sensing and controlling circuit won&#39;t output the high frequency signal under the regular charge mode. At that time, equalization circuit  403  is in static situation (i.e. haven&#39;t any current flow through) because there is not any signal to trigger switches S 1 , S 2 , S 3 , S 4 , which makes switches S 1 , S 2 , S 3 , S 4  all in “off” status. Hence, all of the current from direct current source I will flow through the series of connected battery strings. When battery voltage sensing and controlling circuit  402  discovers that the terminal voltages of a certain battery in the battery strings (e.g. battery B 1 ) is higher than the others (e.g. the terminal voltages of battery B 2 , B 3 , B 4 ) to a predetermined value (e.g. 0.3 voltage), then output port TS 1  will output a high frequency signal to trigger switch S 1 . The Pulse-Width-Modulated (PWM) signal is the high frequency signal in this embodiment, thus switch S 1  can be turned on and off.  
         [0024]     As the above-mentioned, transformer T becomes a forward type transformer immediately when switch S 1  is driven. At that time, winding N 1  becomes a primary winding in transformer T and windings N 2 , N 3 , N 4  become the secondary windings by induction. The currents are induced from winding N 2  flows from positive end into the positive terminal of battery B 2  for charging and then flow out from the negative terminal of battery B 2  to turns on diode D 2  for forming a loop. The charging currents of battery B 2  are the sum of the currents from direct current source I and the induced currents from winding N 2 . Thus, the purpose of charging battery B 2  by the imbalanced voltages from battery B 1  can be achieved. Furthermore, it can also promote the charging current of battery B 2  by controlling the duty cycle of the Pulse-Width-Modulated (PWM) signals to adjust the magnitude of the induced currents.  
         [0025]     Similarly, the currents induced from windings N 3 , N 4  and charging batteries B 3 , B 4  respectively can also advance the charging effect. The utilization of the forward type transformer in present invention not only makes use of imbalanced power of battery B 1  to advance the charging effect in the other batteries, but also speedily reduces the difference in voltages between each battery by restraining the charging rate in battery B 1 . Naturally, when an irregular condition occurs to the terminal voltages of one or more batteries in the series of connected battery strings, equalization circuit  403  will draw out the currents of these batteries to charge the other batteries. Besides, the magnetizing energy stored in transformer T will be drained out by the induced currents from winding Nk and flow back to the battery string through diode Dk when the switch component is turned off, thus the charging currents flowing to the series of connected battery strings can also be increased, but the main purpose of that is to demagnetize the iron core in transformer T. It is a principle to those skills in the transformer art.  
         [0026]     In the same embodiment, when the battery voltage sensing and controlling circuit determinates the difference in voltages between battery B 1  and the other batteries in the battery strings recovers from over a predetermined value during the operation of equalization circuit  403 , the Pulse-Width-Modulated (PWM) signals from output port TS 1  will be stopped. At that time, switch S 1  is turned off, the operation of equalization circuit  403  is stopped and only the operation of current source I remains to charge batteries B 1 , B 2 , B 3 .  
         [0027]      FIG. 5  shows another preferred embodiment of the present invention. There are four equalization loops and just three batteries B 1 , B 2 , B 3 . Wire  501  and wire  511 , wire  503  and wire  511 , wire  504  and wire  512 , wire  505  and wire  513 , wire  506  and wire  514  should be connected, and then wire  520  should be floating, thus the circuit can operate regularly. Similarly, when there are just batteries B 1 , B 2  in the battery string, wire  501  and wire  511 , wire  504  and  511 , wire  505  and wire  512 , wire  506  and wire  513  should be connected, and then floats wire  502 , wire  503  and wire  514 , thus the circuit can operate regularly. It can be seen that the equalization circuit in present invent can work in different quantity of batteries by different wire connected, which benefits the modularity of the equalization circuit and increases the applications.  
         [0028]     The series of connected battery strings can be utilized in electric bicycles, electric motorcycles, electric automobiles or the other apparatuses powered by battery. The present invention can be used in any apparatus flexibly and makes the operation of series of connected battery strings under the best conditions for increasing the efficiency and life of batteries.  
         [0029]     What are described above are only preferred embodiments of the invention, not for confining the claims of the invention; and for those who are familiar with the present technical field, the description above can be understood and put into practice, therefore any equal-effect variations or modifications made within the spirit disclosed by the invention should be included in the appended claims.