Patent Application
20120187901
This invention relates to a charger.
A charger is a device used to put energy into a secondary power cell or battery by forcing an electric current through it. The charge current depends upon the technology and capacity of the power cell or battery being charged.
A charger is a device used to put energy into a secondary power cell or battery by forcing an electric current through it. Unlike a battery, an ultracapacitor does not have memory effect problems, loss of capacity, or long recharge times as a power cell. As a capacitive element, the ultra-capacitor has no charge/discharge memory effects allowing charging and discharging up to hundreds of thousands of cycles without any effect on the storage capacity. Also with its very low equivalent series resistance (ESR), these components can be charged and discharged at rates far greater than the best of battery technologies. An electronically controlled charger for charging a power cell, such as ultra-capacitor or battery, is developed.
The charger can include an electrical circuit for transferring energy from an energy reservoir to a storage element. The potential difference inherent at the energy reservoir may be substantially different from that of the storage element. The circuit can provide a means to convert the storage of electrical energy from one potential difference to another with theoretically perfect (100%) efficiency. In practice, the actual efficiency (the percentage of energy lost during the transfer) will be less than 100% due to finite resistive losses in the various components of the circuit as well as all wiring and electrical contacts.
In certain embodiments, the storage device can be charged as quickly as possible, since one of the advantages of an ultra-capacitor over a battery as a storage element is that the ultra-capacitor can accept a charge at a higher rate than a battery cell of comparable capacity. That is, an ultracapacitor can charge in seconds, whereas a battery of comparable capacity is limited to tens of minutes to hours to charge to a full state.
The charger injects short high current pulses into the ultra-capacitor. The fastest charge rate can be achieved by injecting current pulses as close together in time as possible. The charge process can happen in a two-step cycle for each charging pulse. First, a switch is closed causing current to flow into the ultra-capacitor though an inductor (i.e., a choke), which limits the current rise time, then the switch is opened, and the energy stored in the magnetic field of the inductor dissipates as additional current flowing into the ultra-capacitor.
Referring to
Referring to
In the event that SW2 is a diode or some other kind of device other than a switch, SW2 will normally be in a forward conduction (high current) mode when SW1 is ‘off’ and in a reverse bias (low current) mode when SW1 is ‘on’.
The circuit can also include a controller for altering the state of SW1 and SW2 depending on the potential difference or voltage across SW1 (Vds), SW2 (Vca), the storage element (Vpm) or some other element in the circuit. The controller may also take into consideration the magnitude of the current in either current path I1 or current path I2.
In one embodiment of the invention, SW1 is a FET, IGBT, BJT, or relay, SW2 is a FET, IGBT, BJT, relay, or diode. The energy reservoir is a capacitor, the storage element is an Electrochemical Double Layer Capacitor (EDLC) ultracapacitor or battery or a hybrid of the two.
In another embodiment, the controller turns SW1 ‘on’, and in the event SW2 is a FET, IGBT, BJT, relay or some other kind of switch, turns SW2 ‘off’. This allows for the magnitude of current in current path I1 to increase, not necessarily linearly with time, to a predetermined value. Once the predetermined magnitude of current is achieved in current path I1, the controller turns SW1 ‘off’ and, if appropriate, turns SW2 ‘on’ thus forcing the current in current path I1 into current path I2. The magnitude of the current in current path I2 then begins to decrease, not necessarily linearly with time, due to a back-voltage applied across the inductor. The origin of the back-voltage is the potential differences across SW2 and the storage element. The magnitude of the current in current path I2 is allowed to decrease to a predetermined value, not necessarily zero, whereupon SW1 is turned ‘on’ again and the cycle is repeated. This process continues until the storage element is sufficiently charged.
In some embodiments, when a collapsing current in current path I2 falls to zero (or nearly), the next cycle can begin. To begin the next cycle, the current is sensed. Traditionally, a small resistor can be placed in series with the current to be sensed and the voltage drop across that resistor is measured to detect when the current has declined sufficiently. But there can be several disadvantages to placing a current sense resistor into the circuit. One problem is that the resistor can get hot, wasting power and therefore reducing efficiency. To overcome this shortcoming, the resistor can be made very small—a fraction of an ohm. One difficulty that can arise from this solution is that it becomes difficult (i.e., more costly) to control the precision of the resistor value, and therefore the accuracy of the current sense mechanism. The method used in the charger described here takes advantage of the inherent forward voltage drop of an already existing flyback diode (SW2) and takes that voltage as an indication of the flow of current due to the collapsing magnetic field.
In some embodiments, referring to
Referring to
In the case of the 120 and 240 V AC chargers, this can be accomplished by a fixed pulse duration and in this case Vds is not used. For the 12 V AC charger, however, the pulse duration can vary depending on the status of the ultracapacitors (Vpm) and Vds can be used to set the pulse duration. Vpm can be used to detect end-of-charge and to shut off the series of pulses to Vgs. Vca can be used to detect when the current through inductor 70 has fallen to zero, then it can trigger the start of another pulse to Vgs.
Referring to
For the 12 Vdc charger, the sum of the voltages across FET 41 and ultracap 50 (˜10V) can be significant compared to the voltage on the storage capacitor 31 (˜12V). In this case the duration of the pulse width to the gate will depend on the charge state of the EDLC ultracap 50. The controller can use either Vds across FET 41 or Vmx across inductor 70, or both, to set the gate pulse duration.
When the current through the FET 41 reaches a predetermined value, FET 41 can be turned off. As shown in
FET 41 can be turned on after the current in inductor 70 reaches a predetermined value, such as zero, which can be detected by monitoring the diode forward voltage (Vac). Thereby, it can also prevent any potential damage to FET caused by high currents at high voltages.
As shown in
The charger can include an inductor connected in series with the power cell. A power cell charging cycle can include a current increasing period. The power cell charging cycle comprises a current decreasing period, after the current value reaches a predetermined value.
In one aspect, a method of charging a power cell can include charging the power cell with a first charging current flowing through a first charging circuitry, wherein the first charging current is increasing, and charging the power cell with a second charging current flowing through a second charging circuitry after the first charging current reaches a predetermined current value. The second charging current can be decreasing. The method can include charging the power cell with the first charging current flowing through the first circuitry after the second charging current reaches zero.
The method can include monitoring the voltage across a switch component of the second charging circuitry during charging the power cell with the second charging current. The method can further include switching back to charging the power cell with a first charging current by changing the status of the switching component when the voltage across the switch component reaches a predetermined value. The predetermined value of the voltage across the switch component can be as low as zero volts. The switch component can include a diode.
The power cell can include at least one ultracapacitor. The power cell can include at least one battery. The method can include rectifying a power input from an alternating current power source.
The method can include generating a pulse to control a transistor to switch from the first charging circuitry to the second charging circuitry. The first charging circuitry and the second charging circuitry can share at least one component. The method can include controlling a charging cycle length by changing the predetermined current value. The method can include storing the rectified power input by a storage capacitor.
In another aspect, a charger for charging an energy storage element can include an energy source at a first potential energy or voltage. The energy source can supply energy to the energy storage element by an electrical current. The energy storage element can be at a second potential energy or voltage. The charger can include at least one switch electrically connected to the energy source for determining whether the electrical current flows along a first current path or a second current path.
The first potential energy or voltage can be different from the second potential energy or voltage. The charger can include an inductor for assisting a low loss conversion of energy between the two different potential energies or voltages. The energy storage element can include at least one ultracapacitor. The switch can include a field effect transistor.
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, although the invention is described in reference to an electronically controlled charger, it can apply to any other suitable charging technique, such as any suitable ultracapacitor charging technique. It should also be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention.
This application claims priority to U.S. Provisional Patent Application No. 61/434,632, filed on Jan. 20, 2011, which is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61434632 | Jan 2011 | US |
