Description

The present invention relates in general to converting electric power, and in particular to converting direct current to direct current.

Background

An electric power converter is device which converts electric energy from one form to another form, e.g. from an Alternating Current, AC, to a Direct Current, DC. Electric power converters may also convert a voltage level or a frequency or a combination of both. The present invention in particular relates to DC to DC converters.

DC to DC are typically used in portable electronic devices such a cellular phone, laptop computer or portable computers but also in Internet-of-Things, loT, devices. In such applications the main power supply often (primarily) comes from a battery. Since many of these devices have electronic circuits and sub-circuits which require different voltage levels from that same battery.

Charge pumps are a specific kind of DC to DC converters which use particular circuit layouts to increase (or lower) the voltage level through several stages. Charge pumps, especially of a particular kind, are known for having a high efficiency in conversion without requiring a large number of electric components. Such high conversion efficiency is a typical requirement within the field of loT devices since lifetime of the device needs to be sufficient that no or almost no battery replacement is required and the footprint and/or bill of materials should be small as well. Replacing the battery is undesirable since it takes time, off-line time of the device, human interference, is relatively costly (when compared to the other basic electric components often used in the device), and above all, is very environment unfriendly.

To decrease the dependency from the battery the popularity of energy harvesters for providing power to the loT devices rapidly increases. The output power and especially the voltage level from the energy harvesters may however not be sufficient for typical loT applications. In view of the above, there is a need for efficient power conversion from a very low voltage level towards a voltage level sufficient for loT device or the like, without requiring elaborate, complex additional components or circuits.

Summary

It is an object of the present invention to provide a DC to DC converter with improved efficiency level.

It is a further object of the present invention, to provide a DC to DC converter with improved efficiency level, with a minimal number of electrical components which is capable of converting a low voltage for example provided by an energy harvester, into a higher voltage for example suitable for powering an loT device.

This object is, in a first aspect of the invention, provided by an electric power converter unit for converting Direct Current to Direct Current, DC-DC, the converter unit comprising:

a single stage DC-DC converting module, arranged for connecting with an energy harvesting module for receiving a low voltage DC input thereof and converting the low voltage into a higher voltage arranged for providing a DC output to a load, such as an Internet of Things, loT, device;

a controller module, arranged for enabling and disabling power conversion of the single stage DC-DC converting module;

an energy storage module, comprising a switch and an energy storage unit, arranged for intermediate storage of energy of the DC output, and for providing the intermediate energy storage to the single stage DC-DC converting module as a DC input; wherein the controller module is further arranged to disconnect the load from the converter unit, active the single stage DC-DC converting module to convert the DC input to the DC output, stored in the energy storage unit, during a first conversion cycle and to drive the switch of the energy storage module for the single stage DC-DC converting module to convert the voltage from the energy storage unit to the DC output during a subsequent second conversion cycle, and wherein the load is connected to the convert unit after the second conversion cycle.

Electric power converters may be arranged to convert an input DC voltage into a certain DC output voltage. The conversion ratio between the input and output voltage level is determined by the configuration of the converter and is limited. The voltage level can only be converted by a maximum ratio, very big ratios, which for example are often required if the energy source provides very low, e.g. mV, voltage levels, and load requires much higher levels, e.g. 1V to 5V.

Most known converters are so called inductive converters which use a continuous mode of operation. They have conversion ratio limit of approximately 20. Hence a conversion factor of N between 1 and 20. For loT or WSN device that are powered (primarily) from an energy harvesting source, this is insufficient.

To increase the conversion factor, a cascade of converter circuits may be used. Such a double staged converter however not only leads to lower performance, it also significantly increases (doubles) the required number of electric components.

It was the insight of the inventors to use and re-use the same single converter and include an energy storage module which comprises at least an energy storage unit and a switch for operating said module and therewith connecting said energy storage unit for charging thereof upon a first conversion cycle. At the end of the first cycle the energy (voltage) in the storage unit is used as input on the same single converter to further increase the voltage level to obtain a further increase of the conversion factor. During these cycles, the load is disconnected from the converter and once the first and second cycle are finished, the load is connected again.

In a further example, the controller is arranged for a third, or even fifth, sixth of further conversion cycle following the second cycle and prior to connecting the load.

Each of the conversion cycles separately can provide a certain conversion factor N1 and N2, which may typically range from 2 to 32 times. The total conversion factor N total = N1*N2, wherein N1 being the first conversion factor, and N2 the second. With the converter according to the first example, the conversion factor of N total = Nmax ² can be obtained.

In an example, the single stage DC-DC converting module is arranged for providing a conversion with a conversion factor of N total = N max ² , wherein N max is the maximum conversion factor of the single stage DC-DC converting module.

The converter according the present invention may have a total conversion factor that is higher than a (single stage) converter which is placed in cascade with a further (single stage) converter to form a double stage converter, without requiring a large number of additional components and without affecting power efficiency.

In an example, the converter further comprises a pre-charge module, arranged for providing a pre-charge voltage to the load during a pre-charge cycle, and wherein the controller module is arranged for controlling the pre-charge module for initiating a pre-charge cycle prior to the first conversion cycle.

In an example, the pre-charge module is having a high input impedance for increasing the input impedance of the converter unit during the pre charge cycle.

The pre-charge is typically highly suitable for loT devices or the like which are powered by energy harvesters. In such applications, the loT device may have several power consumption levels, e.g. during a sleep and during an active mode in which for example the high-power demanding RF transmitter becomes active. The pre-charge module makes the converter highly suitable for such applications.

In an example, the single stage DC-DC converting module is arranged for converting a DC input from an energy harvesting module and the pre charge module is arranged for converting a DC input from a battery.

In an example, the load is disconnected during the pre-charge cycle, during the first conversion cycle, and during the second conversion cycle, and wherein the load is connected in an active load cycle following the pre-charge, first and second conversion cycles.

In a second aspect, there is provided, an energy harvesting device, arranged for harvesting energy from at least one external source such as solar, thermal, wind, salinity, kinetic, RF energy, for powering an Internet of Things, loT, or Wireless Sensor Node, WSN device, the energy harvesting device comprising:

an energy harvesting module for harvesting energy from the external source and providing a DC output to an electric power converter unit,

an electric power converting unit for converting the DC output into a DC output for the loT or WSN device; the electric power converting unit comprising an electric power converting unit according to any of the previous descriptions.

The above-mentioned and other features and advantages of the disclosure will be best understood from the following description referring to the attached drawings. In the drawings, like reference numerals denote identical parts or parts performing an identical or comparable function or operation.

Brief description of the drawings

Figure 1 shows in an schematic manner a circuit layout of a DC to DC converter according to a first aspect of the invention.

Detailed description of the drawings

Figure 1 schematically depicts a structure of the novel DC-DC converter where the reference figures depict:

1 An energy cell; e.g. battery, charged supercapacitor, a complementary energy harvester.

2 an energy harvested source.

3 A single stage DC-DC converter.

4 An energy storage for intermediate voltage.

5 a load output energy storage element.

6 a pre-charge switch.

7 A switch for intermediate energy storage

8 a 1 st output switch.

9 a 2nd output switch.

10 an Input switch.

Fig. 2 depicts a sequence of the cycles used in the novel converter The novel DC-DC converter as shown in figure 1 is using switch 8 to connect an energy storage for intermediate voltage (4) during 1 st conversion cycle. During this cycle the switch 10, and 8 are closed and the switch 9 and 7 are open. Such switch configuration allows to convert input Voltage according to the conversion factor; Voutl = Vin *N 1 , where

N1 = Vout (1st cycle) / Vin;

During the 2nd conversion cycle the switches 10 and 8 are open and switches 9 and 7 are closed. That means that the energy storage for intermediate voltage (4) is acting as input voltage source during the 2nd conversion cycle. Vout2 = V intermediate * N2. Where N2 is a conversion factor during the 2 ^nd conversion cycle. This means that the novel DC-DC converter provides a conversion factor of N conversion = N1*N2. It means that the single stage DC-DC converter allows to achieve conversion factor N = Nmax ² and Nmax is the maximal possible conversion factor of the single stage DC-DC converter working in conventional mode.

During the pre-charge cycle, which is normally active before 1 st conversion cycle, the load output energy storage element (5) is pre-charged up to necessary output voltage level when the switch 6 is closed.

Expressions such as“comprise”,“include”, “incorporate”,“contain”, “is” and“have” are to be construed in a non-exclusive manner when interpreting the description and its associated claims, namely construed to allow for other items or components which are not explicitly defined also to be present. Reference to the singular is also to be construed in be a reference to the plural and vice versa.

Furthermore, the invention may also be embodied with less components than provided in the embodiments described here, wherein one component carries out multiple functions. Just as well may the invention be embodied using more elements than depicted in the Figures, wherein functions carried out by one component in the embodiment provided are distributed over multiple components.

A person skilled in the art will readily appreciate that the stages of the comparator comprise switches and that these switches can be embodied by several types of switches known in the art, such as but not limited to transistors, field-effect transistors, MOSFET, NMOS, etc.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single stage of the circuit or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.