Patent Application
20190320641
Applicant claims priority under 35 U.S.C. § 119 of German Application No. 10 2018 003 199.4 filed Apr. 19, 2018, the disclosure of which is incorporated by reference.
The invention relates to weed inactivation device, comprising at least two electrodes, whereby the at least one electrode is directed to the weed. The weed activation device is used as a physical herbicide apparatus.
A weed activation device of the generic type has been disclosed in the yet unpublished international patent application PCT/IB2017001456. According to PCT/IB2017001456 a high voltage is created by the utilization of high voltage transformers. The high-voltage in the range of 1 kV to 20 kV is applied to an electrode which contacts the weed to be controlled or which is brought close to the weed. This physical herbicide has the great advantage of not utilizing chemical herbicides, which may proliferate into the food chain up to humans.
It is an object of the current invention is to provide for a circuitry, which allows use of small, cheap and available electronic components to comprise a high power-factor converter that controls for power without the need of software or other larger components required in previous technological generations. This particular converter is composed of at least the following components: An inverter, an inductive and or capacitive harmonic filter, a capacitive voltage multiplier composed of diodes and capacitors.
Therefore, a weed inactivation device is proposed, comprising at least two electrodes, whereby the at least one electrode is directed to the weed and is supplied with electrical energy by at least one electrical power supply. The at least one electrical power supply could as an example comprise an AC current supply having a frequency in the range of 30 Hz to 90 Hz, preferably in the range of 50 Hz to 60 Hz, and whereby the AC current is rectified by a full-wave rectifier, creating pulsed DC current doubling the AC frequency.
According to the invention a weed activation device is proposed, which is operated with any power supply available.
The power supply is fed to an inverter such as a full or half bridge inverter to create a high frequency current of different frequency than the input current. This current from the inverter can be conducted to a high frequency transformer, whereas the output voltage of the high frequency transformer is in the range of 1 kV to 12 kV and then the output current is the multiplied by a voltage multiplier such as a hexuplicator of the Cockroft-Walton type. Alternatively, the output from the inverter can be fed directly to the voltage multiplier. The multiplier makes it unnecessary to utilize higher voltage transformers, which out up a high demand on electrical insulation of the coiling wires and the connection wiring. The output of the hexuplicator is then conducted to the electrodes for electrical weeding.
A different topology for the electronic converter proposed before can be made for monophasic circuits, as shown in
The topology elements are listed below:
For example, with the use of a voltage doubler as the voltage multiplier fed by the transformer's secondary, the isolation issues for the transformer's high voltage operation is reduced, as well as the number of turns necessary to achieve the desired voltage levels, facilitating the transformer's construction and reducing its size, weight and volume, that were already reduced for the high frequency operation.
Adjusting the inductor and/or inductive/capacitive filter value so the inverter's IGBT can work with resonant switching reduces its conduction losses and increases the converter's efficiency. The IGBT's resonance frequency is tuned as the resonance between the external inductor and the total capacitance reflected to the transformer's primary or directly to the voltage multiplier, considering the effects of the variable load and the voltage multiplier.
The invention will be explained with reference to the drawings. It is to be understood that the drawings are for reference only and are not to be considered limiting of the invention. In the drawings, wherein similar reference numerals constitute similar elements:
An example of the circuit providing the current for the weeding device is shown in
The example topology as shown in
The external inductor reflected to the transformer's secondary side will also provide an impedance matching with the voltage doubler series impedance, and this association with the “plant resistance” will be seen by the transformer as a resistance in parallel with a capacitor inversely proportional to this resistance value. The output voltage will be variable with the resistive load, once the voltage doubler capacitor charging will be “controlled” by the total series impedance seen by him, like that different power values will be delivered by the converter, depending on the resistive load, according to the basic power equation P=V2/R, where R, V and P are the resistive load, its voltage and its power dissipation, respectively. As the impedance matching happens in self-adjustable way, this converter topology presents a self-adjustable power control without the necessity of a control strategy implementation.
The impedance seen by the transformer is still a resistance in parallel with a variable capacitor, as described before. The inverter's resonance switching can be tuned so the converter delivers the optimum maximum power to a specific impedance value. The output power is variable for the same reason as described for the voltage doubler, but for different orders voltage multipliers, all the multipliers capacitors charging must be taken in consideration.
The voltage multiplier series impedance partially solves the problem of transformer series resonance excitation, once the transformer's secondary is never in a real open circuit situation with this new topology.
When the resistive load tends to a low value (short-circuit situation), the voltage multiplier presents a series impedance reflected to the primary that, associated with the external inductor, protects the transformer against high short-circuit currents. When the load tends to a high value (open circuit situation), all the capacitors of the voltage multiplier are charged, increasing the secondary voltage peak, but still limiting it to a maximum value equals the multiplier stage (6, in the case of the hexuplicator).
Another strategy to protect the transformer against this dangerous operation is the addition of an adequate capacitive or a capacitive inductive filter after the external inductor, as shown in
As the “plant resistance” deviates from the tuned value, the delivered power decreases from its optimum maximum value, but a considerable range of power values is still delivered to a great variety of resistive loads, as can be seen in Table below, that show the power delivered to different values of resistive loads, considering power grid as power supply and a capacitive voltage hexuplicator. It's important to notice that the electronic converter as described was never used before for the invasive plant control.
The electronic converter as described before is optimized for monophasic low and medium power applications, so it's ideal for manual applications, nevertheless the topology can be adapted for high power applications, using high power sources, as DC or tri-phasic sources, and tri-phasic rectifiers, as already described in the other topologies.
In this case maybe a full-bridge inverter can be more adequate to deliver power levels necessary. Another modification that can be interesting for high power applications is the used of high frequency transformer with a centered tap at its secondary winding, as shown in
As a general description of the system, a DC or AC power supply of any number of phases generates a voltage. This voltage is fed to an inverter that increases frequency. The current with increased frequency is fed to a harmonic filter (inductive, capacitive or both) that ensures a high power-factor, diminishing or excluding the need of a separated PFC. The inductive and/or capacitive harmonic filter may feed a high frequency transformer that further increases the voltage input for the voltage multiplier. The high frequency transformer may comprise a centered tap at its secondary winding, which can serve as a voltage reference or grounding to the secondary coil. The output of the previous components is fed to a voltage multiplier, such as a voltage multiplier of the Cockroft-Walton type or a full wave Cockroft-Walton type, such as a hexuplicator, multiplying the input voltage by a factor of six. The voltage multiplier provides different voltage levels depending on its load, so for a variable load it makes an auto-adjustable power control without any additional circuitry, processor or controller necessity. If, as described, a transformer was necessary to further increase the voltage be-tween the harmonic filter and the voltage multiplier, the voltage multiplier always represents a series impedance connected at the transformer secondary, not letting the transformer in a direct real open circuit situation, reducing the risks of series resonance excitation and voltage peaks that could damage insulation or create other internal damages.
This particular construction allows for the inverter switching to be set as resonant or quasi-resonant. This setting of the inverter as resonant or quasi-resonant, reduces its output harmonic composition, reducing the risk of transformer series resonance excitation and, consequently, reducing the risk of compromise the transformer insulation. Also, the inverter's switches (like, but not limited to IGBTs, power transistors, mosfets) have reduced conduction losses when working in the resonant or quasi-resonant mode, increasing the converter's overall efficiency.
In
The topology of
In
Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 003 199.4 | Apr 2018 | DE | national |
