Electric energy converter unit with maximum power point tracking (MPPT) for converting direct current to direct current (DC-DC) for maximum possible efficiency

Abstract

The invention relates to an electrical energy converter unit with maximum power point tracking for converting direct current to direct current, i.e. DC-DC, for measuring the converted power at the output and controller module.

Description

[0001] This application is a divisional application of the patent application with the application number 2020800236747, the application date of January 30, 2020, and the invention title of "Power converter unit with maximum power point tracking (MPPT) for converting direct current to direct current, i.e., DC - DC, to obtain the maximum possible efficiency". Technical Field

[0002] The present invention relates to a power converter unit for converting direct current to direct current (DC - DC) having a maximum power point tracking for measuring the converted output power and regulating electrical parameters using a controller module. Background Art

[0003] Existing solutions use a power converter unit for converting direct current to direct current having an inductor and a maximum power point tracking, where the maximum power point tracking adjusts the input impedance of the power converter based on the input voltage measurement. The disadvantages of the power converter unit for converting direct current to direct current are the complexity of the design, the occupied space size of external components (such as inductors, etc.), and the sensitivity to pulse control signals. The main defect of the maximum power point tracking for adjusting the input impedance of the power converter unit based on the input voltage measurement is that the efficiency of the power converter unit is not considered during the tracking calculation. Some maximum power point tracking circuits adjust the input impedance of the power converter unit based on the output voltage measurement. However, this method depends to a large extent on the capacitance connected at the output of the power converter unit. Summary of the Invention

[0004] In view of the above - mentioned disadvantages, an object of the present invention is to provide an improved power converter unit for converting direct current to direct current based on switched - capacitor technology, including a maximum power point tracking for measuring the output of the power converter unit and the converted power at the controller module.

[0005] Another object of the present invention is to provide such a power converter with improved energy efficiency, where the energy consumed by the control of the maximum power point tracking is reduced compared to known power converter units.

[0006] According to a first aspect of the present invention, there is provided an electrical energy converter unit including a power detector. A switched capacitor electrical energy converter unit for converting direct current to direct current enables large-scale integration of the device and a very small assembly size. Further, since the power detector included in the present invention measures the output current rather than the voltage, the power detector allows the use of high capacitor energy storage. In an embodiment, the output current of the switched capacitor electrical energy converter unit is driven by a programmable resistor, thereby generating a voltage drop of the first potential difference and the second potential difference across the resistor. Further, the voltage drop across the resistor is amplified by a voltage amplifier and sampled by a sample-and-hold comparator. The sample-and-hold comparator reads the amplified voltage drop and compares the two samples. The output of the sample-and-hold comparator enters a state machine, which determines whether the electrical energy converter unit parameters must be changed to increase the output power. The parameters are changed by a controller module for controlling the switching frequency and voltage gain of the electrical energy converter unit.

[0007] In energy harvesting systems such as RF energy harvesting modules, and PV-based energy harvesting modules, very low energy levels are captured from the energy source. Therefore, extremely efficient power management control is required to convert electrical energy from the energy harvesting source to a load (e.g., an Internet of Things sensor). Known maximum power point trackers typically use dedicated microcontrollers for measuring the maximum power point. Compared to the applications of (e.g., RF-based) energy harvesters, these microcontrollers consume a large amount of energy, which makes these microcontrollers not very efficient and suitable for such applications.

[0008] In an embodiment, an electrical energy converter unit including a DC-DC conversion module, a controller module, and a maximum power point tracking module is fully integrated as a system-on-chip SoC. This enables high power efficiency and sub-microwatt power consumption of the electrical energy converter. There is no need for an additional low-power efficiency microcontroller to measure the maximum power point of the power supply input connected to the DC-DC conversion module.

[0009] In an embodiment, the electrical energy converter unit is configured to subsequently turn on and off the maximum power point tracking module.

[0010] In an embodiment, the electrical energy converter unit is configured to subsequently turn on and off the current to the resistor.

[0011] In an embodiment, the electrical energy converter unit is configured to simultaneously turn on and off the maximum power point tracking module and the current to the resistor.

[0012] In another embodiment, the power converter unit is configured for power gating of a maximum power point tracking module assembly (such as the maximum power point tracking module itself and also preferably a resistor, etc.). This is achieved by subsequently deactivating and enabling the power point tracking module and / or (but preferably simultaneously) deactivating and enabling the current through the resistor to reduce power consumption. Thus, deactivating the maximum power point tracking can be achieved, for example, by bypassing the current to the resistor directly from the output of the DC-DC conversion module to the load, where the resistor is connected in series with the electrical output of the DC-DC conversion module. Thus, deactivating the maximum power point tracking can also be achieved by deactivating the maximum power point tracking module itself. Most preferably, simultaneous on and off timing and time intervals are used to deactivate both at the same time. Thus, in the most preferred embodiment, the state machine disconnects the maximum power point tracking and shorts / programs the sense resistor to ensure low power operation.

[0013] Preferably, the resistor is one of an adjustable resistor or a programmable resistor. In another example, the maximum power point tracking can be deactivated by adjusting or programming the resistor with a zero-value.

[0014] In an example, at least one state machine (preferably a synchronous state machine) is configured for power gating of the maximum power point module. At least one state machine can be included in the maximum power point tracking module or the controller module.

[0015] Using any embodiment that deactivates the current flowing through the resistor for at least a period of time, discontinuous measurement results are obtained. Compared with known solutions that are typically based on continuous measurement results, the maximum power point tracking module in any of these aspects or embodiments achieves improved power consumption efficiency.

[0016] Using power gating of the maximum power point tracking module, sub-microwatt power consumption of the power converter unit is achieved. Power gating ensures that no power is dissipated in the resistor while converting energy.

[0017] The duty cycle of the power gating can be changed. For efficient power consumption, the time slot with maximum power tracking enabled is small, and the time slot with maximum power tracking disabled is large, preferably with a duty cycle of 10%, more preferably less than 5%. In other words, the ratio between the on-time and off-time of the maximum power point tracking module or at least the ratio between the on-time and off-time of the current flowing through the resistor is at least 1:2, but more preferably 1:4, 1:8, 1:10, 1:20 or even higher. More preferably, the ratio is dynamic and can change over time.

[0018] Using this duty cycle, sub-microwatt power consumption during energy conversion is achieved without continuously enabling the maximum power point tracker. The decision on the maximum power point is made during an hourly slot preferably not exceeding 1 second. In yet another embodiment, the electrical energy converter unit is configured to detect whether there is no power delivered to the output of the DC-DC conversion module, for example due to a power outage, and to stop the energy conversion. Preferably, this is done by at least one state machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will now be described in a non-limiting manner with reference to the accompanying drawings, in which like parts are indicated by like reference numerals, and in which:

[0020] Figure 1 is a high-level block diagram of the present invention.

[0021] Figure 2 is a block diagram of maximum power point tracking.

[0022] Figure 3 is Embodiment 1 of a voltage amplifier.

[0023] Figure 4 is a timing diagram of maximum power point tracking operation. DETAILED DESCRIPTION

[0024] Figure 1 A block diagram depicting an electrical energy converter unit for an energy harvesting application is shown, the electrical energy converter unit including a DC-DC conversion module (100), maximum power point tracking (102), a sample and hold comparator (103), an oscillator / controller module (101), and an energy harvesting transducer (104).

[0025] The DC-DC conversion module (100) converts the energy provided by the energy harvesting transducer 104. Electrical parameters such as impedance and power of the energy harvesting transducer 104 change over time due to weather conditions, line of sight, or mobility conditions. Therefore, a control loop is needed to adapt the electrical parameters of the DC-DC conversion module to the electrical parameters of the energy harvesting transducer 104.

[0026] The impedance of the DC-DC conversion module 100 is controlled by the maximum power point tracking and oscillator-controller module (101). In the maximum power point tracking 102, the output current of the DC-DC conversion module is converted to a voltage, which is sampled in the sample and hold comparator (103). Additionally, two sampled voltages are successively compared in the sample and hold comparator 103, and the sample and hold comparator outputs a digital signal, which is read by a state machine built into the maximum power point tracking 102. The state machine reads the comparator signal and sets the control bits of the DC-DC conversion module 100 and the oscillator / controller module 101.

[0027] The control bits are intended to adjust the voltage gain of the DC-DC conversion module 100 and the switching frequency defined by the oscillator / controller module 101, and thereby adjust the electrical parameters of the DC-DC conversion module.

[0028] Figure 2 A block diagram showing the maximum power point tracking 102 including a low-pass filter (105), a voltage amplifier (106), a programmable resistor (107), a sample-and-hold comparator (103), and a state machine (109). The output current of the DC-DC conversion module flows through the resistor 107, which has a first terminal connected to the low-pass filter 105 and a second terminal connected to the output. The low-pass filter 105 allows the average output current to be converted into a DC voltage, which is amplified by the voltage amplifier 106. Subsequently, the sample-and-hold comparator 103 samples the amplified voltage and compares it with the previously sampled voltage. After this comparison, the sample-and-hold comparator 103 outputs a logic signal that is read by the state machine 109, which determines whether to increase or decrease the bit count of the oscillator / controller module and the bit count of the DC-DC conversion module gain.

[0029] Figure 3 An embodiment of the voltage amplifier 106 is shown. The voltage amplifier 106 includes an operational amplifier (110), an input resistor (111), and a feedback resistor (112). The voltage gain of the voltage amplifier 106 is defined by the ratio between the feedback resistor 112 and the input resistor 111.

[0030] As a second embodiment, a circuit can be implemented using a buffer to drive the input resistor 111 Figure 3 In addition, the input resistor 111 and the feedback resistor 112 can be replaced by a switched-capacitor network including an input capacitor and a feedback capacitor, and the gain is set by the capacitance ratio.

[0031] Figure 4Shows a time graph of maximum power point tracking as an example of an algorithm implementation. The control signal 113 changes with a duration T1 called the settling interval, and the control signal 113 changes during a period of T2 seconds called the scan interval. The control signal 113 defines the frequency parameter of the DC-DC conversion module (100). Subsequently, the control signal 114 is scanned during a period of T3 seconds called the fine-tuning interval. When the maximum power point is detected at the output of the DC-DC conversion module, the control signals 113 and 114 are considered to be at the optimal values. The duration T4 is the time of a sleep interval during which the maximum power point tracking is disconnected. Generally, the sleep interval T4 is much longer than the active interval which is the sum of T1, T2, and T3, in order to reduce the average power consumption of the maximum power point tracking and improve the system efficiency. The settling interval T1 is constant. On the other hand, the scan interval T2 and the fine-tuning interval T3 can change according to the number of steps required to find the maximum power point of the DC-DC conversion module.

Claims

1. An electrical energy converter unit for converting direct current to direct current (DC - DC), comprising: a DC - DC conversion module operable to be connected to an energy harvesting module for supplying an electrical input to the DC - DC conversion module and outputting an electrical output for connection to a load; a controller module operable to electrically control the DC - DC conversion module and control electrical parameters of the DC - DC conversion module, wherein the electrical parameters at least include the input impedance of the DC - DC conversion module; and a maximum power point tracking module coupled to the controller module and operable to output a power point control signal to the controller module to adjust at least one of the electrical parameters, wherein the maximum power point tracking module includes a resistor connected in series with the electrical output for connecting the load of the DC - DC conversion module, and provides the power point control signal to the controller module based on a comparison between a first voltage potential sample and a second voltage potential sample across the resistor, and wherein the first voltage potential and the second voltage potential are sampled sequentially in time.

2. The electrical energy converter unit according to claim 1, wherein, the electrical energy converter unit is operable to subsequently turn on and off the maximum power point tracking module.

3. The electrical energy converter unit according to claim 1, wherein, the electrical energy converter unit is operable to subsequently turn on and off the current to the resistor.

4. The electrical energy converter unit according to claim 2, wherein, the electrical energy converter unit is operable to simultaneously turn on and off the maximum power point tracking module and the current to the resistor.

5. The electrical energy converter unit according to claim 3, wherein, the maximum power point tracking module further includes a bypass circuit for bypassing the resistor, wherein the current to the resistor is turned off.

6. The electrical energy converter unit according to claim 1, further comprising a duty cycle for turning on and off one or more of the currents to the resistor and turning on and off the maximum power point tracking module, the duty cycle being at most 50%.

7. The electrical energy converter unit according to claim 1, wherein, the output current of the DC - DC conversion module is measured by determining the first voltage potential sample and the second voltage potential sample across the resistor.

8. The electrical energy converter unit according to claim 1, wherein, the DC - DC conversion module is a switched - capacitor DC - DC converter.

9. The electrical energy converter unit according to claim 1, wherein, the resistor is an adjustable resistor or a programmable resistor.

10. The electrical energy converter unit according to claim 1, wherein, the resistor is a part of the output resistance of the DC - DC conversion module.

11. The electrical energy converter unit according to claim 1, wherein, the controller includes an oscillator.

12. The electrical energy converter unit according to claim 1, wherein, The electrical parameter further includes one or more of the voltage gain and the switching frequency of the DC-DC conversion module.

13. The electrical energy converter unit according to claim 1, wherein, the voltage drop between the first voltage potential and the second voltage potential is amplified by a voltage amplifier.

14. The electrical energy converter unit according to claim 13, wherein, the voltage amplifier is a switched capacitor amplifier.

15. The electrical energy converter unit according to claim 14, wherein, the maximum power point tracking module further includes a low-pass filter for smoothing at least one of the first voltage potential signal and the second voltage potential signal.

16. The electrical energy converter unit according to claim 1, wherein, the maximum power point tracking module further includes a sample-and-hold comparator for sequentially sampling the first voltage potential and the second voltage potential in time.

17. The electrical energy converter unit according to claim 1, wherein, the maximum power point tracking module further includes a state machine for determining that one or more of the electrical parameters must be changed.

18. The electrical energy converter unit according to claim 17, wherein, the state machine determines to adjust the bit count of one or both of the controller module and the DC-DC conversion module.

19. A system-on-chip (SoC) includes the electrical energy converter unit according to claim 1.

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