Patent Application
20130162214
1. Technical Field
The invention relates to a capacitor active balancing device and the method thereof. In particular, the invention relates to a capacitor active balancing device with high-voltage differential that has at least two cells connected in series to charge an energy storage unit and utilizes the energy storage unit to transfer energy, as well as the method thereof.
2. Related Art
In recent years, the popularity and prosperous development of secondary battery (also known as rechargeable battery) bring wide applications in such vehicles as hybrid cars, fuel battery cars, electric cars, etc. However, batteries may degrade rapidly under various kinds of environments. It is therefore an imperative issue for vendors to increase the lifetime of batteries.
Generally speaking, a battery consists of several cells connected in series. Since each cell may have different material properties from the others, it is likely to have overcharge/overdischarge during charging/discharging processes, affecting the lifetime of the battery. To avoid this problem, the battery balancing technique is employed to moderate energy among the cells so that all of them reach their threshold voltage simultaneously during the charging process. Currently, the technique can be divided into active balancing and passive balancing. Due to its small energy loss and little heat generation, the active balancing receives a lot of attention. Commonly seen active balancing styles include capacitor balancing and inductor balancing. The former has a lighter weight and lower efficiency, whereas the latter has a heavier weight and higher efficiency. The inductor balancing has thus become the current mainstream. However, under the consideration of weight, the importance of capacitor balancing cannot be overlooked.
In the capacitor balancing technique, some vendor proposes to use programmable control logic to control an arbitrary pair of switches (i.e., the paired switches that connect the positive and negative poles of a cell) to balance the voltage between the capacitor and the cell. It can freely control the on/off time of the switches. Nevertheless, the above-mentioned method applies only to the battery balancing of a single cell and a capacitor. It cannot effectively solve the problem of low efficiency in battery balancing.
In summary, the prior art always has the problem of low efficiency in capacitor battery balancing. It is thus desirable to provide a solution.
In view of the foregoing, the invention discloses a capacitor active balancing device with high-voltage differential and the method thereof
The disclosed capacitor active balancing device with high-voltage differential includes: a plurality of cells, a switch control unit, and an energy storage unit. N cells are connected in series for storing and providing electrical power, where N is a positive integer no less than 2. The switch control unit electrically connects to the cell series for switching and forming a power supply series of K cells connected in series in a first state and for switching and forming a power charging series of L cells connected in series in a second state. Here K and L are positive integers and N≧K≧2, K−1≧L≧1. The energy storage unit electrically connects to the switch control unit for receiving and storing electrical power from the power supply series in the first state, and for outputting the electrical power of the energy storage unit to charge the power charging series in the second state.
The disclosed method of capacitor active balancing with high-voltage differential includes the steps of: providing N cells connected in series to form a cell series for storing and providing electrical power, where N is a positive integer no less than 2; when the switch control unit is in a first state, switching the electrical connection to the cell series to form a power supply series of K cells, where the power supply series output electrical power to the energy storage unit for storage and K is a positive integer and N≧K≧2; when the switch control unit is in a second state, switching the electrical connection to the cell series to form a power charging series of L cells, where the energy storage unit outputs electrical power to charge the power charging series and L is a positive integer and K−1≧L≧1.
As described above, the invention differs from the prior art in that the invention has several cells connected in series to charge the energy storage unit under high-voltage differential. The energy storage unit discharges cells of lower power to complete energy transfer and battery balancing.
Using the above-mentioned technique, the invention achieves the goal of increasing battery balancing efficiency.
The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein:
The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.
Before describing the disclosed capacitor active balancing device with high-voltage differential and the method thereof, we first explain terms used herein. The cell series refers to N cells connected in series, where N is a positive integer no less than 2, such as 2, 3, 4, etc. The power supply series refers to K cells connected in series for charging the energy storage unit. The power charging series refers to L cells connected in series for receiving and storing electrical power from the energy storage unit. Here K and L are positive integers, with N≧K≧2 and K−1≧L≧1.
Suppose N=3, then K=3 or 2 and L=2 or 1. Generally speaking, the electrical power in cells of the power supply series is higher on the average. However, it is not excluded that the power supply series may contain cells with electrical power lower than the average.
The switch control unit 20 electrically connects to the cell series 100. It switches the electrical connection with the cell series 100 in a first state, thereby forming a power supply series of K cells (not shown). The first state is the state of transferring electrical energy from the cells 10 to the energy storage unit 30. When to transfer electrical energy is determined by the amount of electrical energy in each of the cells 10. In a second state, the switch control unit 20 switches the electrical connection to the cell series 100 to form a power charging series (not shown) of L cells 10. Here K and L are positive integers with N≧K≧2 and K−1≧L≧1. The second state is the state of transferring electrical energy from the energy storage unit 30 to the power charging series. For example, suppose N=4 and K=2. Then the number of cells 10 in the power charging series L=1 (that is, 2−1≧L≧1). Suppose N=4 and K=3, the number of cells 10 in the power charging series is 2 or 1. Whether the number of cells 10 is 2 or 1 is determined by the electrical power in the cells 10. To charge the cell 10 with the lowest electrical power, the number of cells in the power charging series is then 1. To charge all cells 10 with lower electrical power, the number of cells in the power charging series is then 2. In practice, the switch control unit 20 may consist of a microcontroller and several switches. Cells 10 with electrical power lower than the average may connect with other cells 10 in series to form the power supply series. Cells 10 with electrical power higher than the average may connect with other cells 10 in series to form the power charging series. The switch can be a metal-oxide-semiconductor field effect transistor (MOSFET). After the control selects the first or second state, the controller controls the on and off of the switch so that the cells 10 and the energy storage unit 30 form a suitable charging/discharging circuit. Generally speaking, the residual electrical power of each cell 10 may vary with time. Therefore, the switch control unit 20 alternates between the first and second state. The cells as the power supply series and power charging series and the number thereof also vary with time. The method of using the switch control unit 20 to form the power supply series and power charging series will be described in detail with reference to accompanying drawings later.
The energy storage unit 30 electrically connects to the switch control unit 20 for receiving and storing electrical power from the power supply series in the first state. That is, the power supply series formed by the switch control unit 20 in the first state has high-voltage differential with the energy storage unit 30. Therefore, the power supply series charges the energy storage unit 30. In the second state, the switch control unit 20 already finishes the switch and forms the power charging series. The electrical energy of the power charging series is lower. The energy storage unit 30 thus outputs electrical power to the power charging series for charging. This completes the procedure of using the energy storage unit 30 to move electrical energy of two or more cells 10 (i.e., power supply series) to cells 10 (i.e., power charging series) with lower electrical energy, thereby achieving active balancing. It should be mentioned that the energy storage unit 30 contains at least one capacitor for storing and providing electrical power. The capacitor may even connect in series to a resistor to form an RC circuit. The resistor can be a capacitor equivalent resistor, normal resistor, switch resistor, battery internal resistor or their combination. The resistance or capacitance of the circuit connected in series with the resistor and the capacitor can be adjusted to set a response time.
An embodiment is explained with reference to
Although an explicit embodiment is used to illustrate the switch control unit 20, 201 with reference to
In summary, the invention differs from the prior art in that multiple cells 10 are connected in series to charge the energy storage unit 30 under high-voltage differential, and that the energy storage unit 30 discharges cells 10 of lower electrical power, thereby completing energy transfer and battery balancing. This technique can solve problems in the prior art and increase battery balancing efficiency.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.
