FREQUENCY ADAPTIVE HARMONIC CURRENT GENERATOR Technical Field of the Invention

The invention relates to a frequency adaptive harmonic current generator. The invention more particularly relates to a frequency adaptive harmonic current generator developed for generating and measuring defined, steady and high- accuracy current harmonics.

Prior Art

In power plants, the generators generate electricity in alternating form. The generated alternating voltage is sinusoidal, i.e. in sinus form. The reason for this is that less harmonic current is generated. In case of excessive harmonic current, on the other hand, too much energy is lost during power transmission and distribution.

Several techniques have been developed in order to reduce the effect of the harmonic currents leading to energy loss.

The U.S. Patent Application No. US7511468 filed on 20.11.2006 within the state of the art discloses a portable instrument for performing in-situ harmonic voltage measurements and harmonic current measurements on alternating current (AC) power conductors. This instrument is designed for in-situ use and a current source is disposed for the calibration of measurement modules inside the instrument prior to use.

Another document in the state of the art is the U.S. Patent Application No. US5656924 filed on 27.10.1995, wherein a system developed for providing harmonic currents to a harmonic generator connected to a multiphase alternating current power system is disclosed. This system includes a zig-zag transformer and a current generator. This device is designed for reducing harmonics in a harmonic generating load.

The fact that there exists no device that generates, measures harmonics and performs such operations without being dependent on a given frequency has deemed it necessary to develop the frequency adaptive harmonic current generator according to the invention.

Objects and Summary of the Invention

The object of the present invention is to provide a frequency adaptive harmonic current generator. Another object of the present invention is to provide a frequency adaptive harmonic current generator which allows measuring current harmonics as well as generating them.

Another object of the present invention is to provide a frequency adaptive harmonic current generator having two separate electrical inputs and enabling the generation and measurement of current harmonics to be more stable and of higher quality.

Another object of the present invention is to provide a frequency adaptive harmonic current generator which has a measurement module for monitoring the generated harmonics. And another object of the present invention is to provide a frequency adaptive harmonic current generator which comprises a microcontroller based circuit and an embedded software.

The current generator according to the invention is designed for generating defined harmonic currents and monitoring the measured values. At the same time, due to the frequency adaptive nature thereof, it can be used for generating and measuring harmonic currents from power supplies in the frequency range of 45 - 65 Hz.

Detailed Description of the Invention

The frequency adaptive harmonic current generator developed for achieving the objects of the present invention is illustrated in the accompanying drawings, in which;

Fig. 1 is the graph showing the defined current harmonics generated by resistive switching technique.

Fig. 2 is the graph showing the change in the triggering signal of the electronic relay depending on the change in the frequency of the applied voltage, and thus the stability of the generated current harmonics.

Fig. 3 is the graph showing the voltage applied by a different trademark device source and the current drawn by the invention from such source.

Fig. 4 is the graph showing the results of the measurement from a different trademark device.

Fig. 5 is the graph showing the results of the measurement from the current generator according to the invention.

Fig. 6 is the graph showing the application of various voltage harmonics at 230 V (RMS) voltage, 50 Hz base frequency to the current generator according to the invention.

Fig. 7 is the graph showing the current harmonics generated from the current generator according to the invention (for the voltage in Fig. 6).

Fig. 8 is the graph showing the application of various voltage harmonics at 230 V (RMS) voltage, 60 Hz base frequency to the current generator according to the invention.

Fig. 9 is the graph showing the current harmonics generated from the current generator according to the invention (for the voltage in Fig. 8). Fig. 10 is the block diagram showing the current generator according to the invention.

Fig. 11 is the front schematic view of the current generator according to the invention.

Fig. 12 is the rear schematic view of the current generator according to the invention.

Fig. 13 is the top schematic view of the inside of the current generator according to the invention.

Fig. 14 is the schematic view of the microcontroller board disposed in the current generator according to the invention.

Fig. 15 is the flow diagram of the embedded software operating on the microcontroller board disposed in the current generator according to the invention.

The parts shown in the drawings are enumerated individually and the corresponding reference numerals thereto are given below.

1. Main power input

2. Power on/off switch

3. Harmonic current withdrawal input

4. Harmonic on/off switch

5. Voltage divider

6. Buffer

7. Rectifier

8. Current shunt

9. High voltage diode

10. TVS diode

11. Electronic relay

12. Resistive load

13. Data collection unit

14. Panel type computer

15. Microcontroller board 16. Switching mode power supplies

17. Cooling fans

18. USB connector

19. LAN connector

20. Button

21. Microcontroller

22. Voltage comparator

23. Resistor

24. Transistor The frequency adaptive harmonic current generator according to the invention comprises: a microcontroller board (15) used for controlling the generation of harmonic currents and frequency adaptive operating function,

an electronic relay (11) controlled and switched over the digital output of the microcontroller (21), the resistor (23) and the transistor (24), a data collection unit (13) to which the voltage divider (5), the buffer (6) and the current shunt (8) are connected for the measurement of voltage and current harmonics and which reads the current and voltage values and transfers such values to the panel type computer (14), and

- a panel type computer (14) which includes software for making, presenting and recording the measurements; the external connections of which are ensured by USB connectors (18) and a LAN connector (19); which displays the measurement values to the user; and which has pushbutton (20) for switching on/off operations. The invention is a frequency adaptive harmonic current generator; wherein it comprises a main power input (1) used to supply the switching mode power supplies (16) and cooling fans (17). The invention is a frequency adaptive harmonic current generator; wherein it comprises a harmonic current withdrawal input (3) that permits applying voltage sources with different voltage and frequency values.

The invention is a frequency adaptive harmonic current generator; wherein it comprises a harmonic on/off switch (4) used for switching on/off the generation of current harmonics.

The invention is a frequency adaptive harmonic current generator; wherein it comprises a bridge type rectifier (7) between the harmonic current withdrawal input (3) and the resistive load (12) in order to generate unidirectional currents at resistive load (12) side.

The invention is a frequency adaptive harmonic current generator; wherein it comprises a power on/off switch (2), which serves as the main on/off switch of the generator.

The current withdrawn by the resistive load (12) connected to the source generating sinusoidal voltage will also be sinusoidal. The main operating principle of the invention is based on the activation/deactivation of the resistive load (12) at each period of the voltage varying in a time-dependent manner and in suitable times, by switching. As a result of this technique, defined current harmonics are generated (Fig. 1). When the load is resistive, the withdrawn current is sinusoidal. In the display of the current in frequency domain, only base frequency component is seen. When resistive load (12) switching technique is applied, the current signal is chopped and is no longer sinusoidal. The withdrawn current in this case comprises many harmonic components. A high-power resistive load (12) is used in the system to generate steady currents. A bridge type rectifier (7) is provided between the harmonic current withdrawal input (3) and the resistive load (12) in order to generate unidirectional currents at resistive load (12) side of the system. Again at the resistive load (12) side of the system, a high voltage diode (9) and a TVS diode (10) are connected for protection.

A microcontroller (21) based electronic circuit is used for switching. This circuit detects zero crossing points and precisely measures the period of the voltage signal using the internal timer thereof. The stability of the current harmonics to be generated is dependent on the switching timing of the resistive load (12). To that end, a timer disposed in the microcontroller (21) starts to count at each zero crossing of the voltage signal and the electronic relay (11) connected to the resistive load (12) is switched at time points determined according to the counter value.

The output of the main voltage divider (5) is connected to the input of the voltage divider (5) disposed in the microcontroller board (15). What is intended here is to lower the voltage signal to a suitable level prior to applying the same to the voltage comparator (22). Zero crossing detector circuit is formed by the voltage comparator (22) and the resistor (23). The output of the voltage comparator (22) is connected to a digital input of an 8051 based microcontroller (21). A digital output of the microcontroller (21) controls the electronic relay (11) through a resistor (23) and a transistor (24). The entire electronic circuit is supplied by 5V DC voltage.

The precisely measured time period value of the voltage signal is used for frequency adaptive operating function. The only way to generate the same current harmonics at different frequencies is that the duty cycle of the electronic relay

(11) switching signal is steady. Electronic relay (11) switching timing is calculated again for each period based on the previous value of the voltage signal period. Therefore, the durations in which the resistive load (12) is activated are variable, not stable. During this calculation, however, the duty cycle, i.e. the ratio between the measured time period and the time during which the resistive load

(12) is activated, is kept stable. The triggering timing of the electronic relay (11) changes as a result of a change in the voltage source frequency, but not the triggering signal duty cycle (Fig. 2).

It is seen at the top of Fig. 2 that the electronic relay (11) switching signal changes depending on the voltage source frequency. The fact that the duty cycle remains steady also makes the generated current harmonics steady. This is shown in the frequency domain.

A precise current shunt (8) and a precise voltage divider (5) are provided in the invention so as to perform measurements. The voltage divider (5), the buffer (6) and the current shunt (8) are connected to the data collection unit (13) inputs for the measurement of voltage and current harmonics. The data collection unit (13) is connected to the panel type computer (14) via USB connection line. The software produced for making, presenting and recording the measurements is run by this panel type computer (14).

A data collection unit (13) reads the current and voltage values, and then transfers such values to the panel type computer (14). These data are processed and presented to the user. USB connectors (18) and an LAN connector (19) are provided for external connections of the panel type computer (14). A push-button (20) is disposed for starting/shutting down the panel type computer (14).

The main power input (1), on the other hand, is used to supply the switching mode power supplies (16) and cooling fans (17). It must be connected to a 230V / 50Hz network. The power on/off switch (2) serves as the main on/off switch of the generator according to the invention.

The frequency adaptive harmonic current generator is designed for generating and measuring defined, steady and high-accuracy current harmonics. One of the main characteristics of the invention is that the current harmonics can be measured in addition to being generated. The second important characteristic is the frequency adaptive operation. Commercially available harmonic generators may be used in a single determined network frequency (e.g. 50 Hz). The invention, on the contrary, can be used with voltage sources in the frequency range of 45 - 65 Hz and it can continuously generate and measure the same current harmonics. A third important characteristic is the provision of separate electrical power inputs. The invention has two individual electrical power inputs: one main power input (1) to supply the internal systems and one harmonic current withdrawal input (3) for the connection of the voltage source from which the current harmonics will be withdrawn. Thanks to this property, the generation and measurement of current harmonics can be more steady and of higher quality. Additionally, the fact that an individual harmonic current withdrawal input (3) from which current harmonics will be withdrawn permits applying voltage sources with different voltage and frequency values to said input. In fact, this voltage source is not entirely sinusoidal, but it may be a source applying voltage harmonics. During the whole process, the main power input (1) used to supply the internal systems enables the invention to operate steadily based on the stable network voltage. The harmonic current withdrawal input (3) must be connected to the power supply or network from which current harmonics will be withdrawn.

Once the development process of the present invention has been completed, many experimental measurements have been made. Exemplary measurement results are given in Figs. 3, 4, 5 and Table 1. Different trademark measurement instruments are used for this experimental comparison measurements.

The graph illustrated in Fig. 3 shows the voltage applied by a different trademark source and the current drawn by the invention from such source. The applied voltage is 230 V (RMS), 50 Hz.

The comparison of the measurement results obtained with the invention itself and with different trademark measurement instruments regarding the generated current harmonics by the invention are shown in Figs. 4 and 5. Fig. 4 shows the measurement results from a different trademark device while Fig. 5 illustrates the measurement results from the invention.

The current harmonics measurement results shown in Figs. 4 and 5 are also given in Table 1. The maximum difference between the measurement results of the two systems is lower than 0.1 %.

Frequency Adaptive

TESEQ NSG 1007-45 Harmonic Current

Generator

Harmonic Current Current Current Current Difference Difference No. (IRMS amp) (%) (IRMS amp) (%) (IRMS amp) (%)

1 1.596 100.00 1.5859 100.00 0.0101 0.00

2 0.003 0.19 0.0022 0.14 0.0008 0.05

3 0.908 56.89 0.9034 56.96 0.0046 -0.07

4 0.002 0.13 0.0015 0.09 0.0005 0.03

5 0.083 5.20 0.0831 5.24 -0.0001 -0.04

6 0.001 0.06 0.0014 0.09 -0.0004 -0.03

7 0.311 19.49 0.3093 19.50 0.0017 -0.02

8 0.002 0.13 0.0022 0.14 -0.0002 -0.01

9 0.182 11.40 0.1812 11.43 0.0008 -0.02

10 0.001 0.06 0.0007 0.04 0.0003 0.02

11 0.105 6.58 0.1046 6.60 0.0004 -0.02

12 0.002 0.13 0.0021 0.13 -0.0001 -0.01

13 0.179 11.22 0.1782 11.24 0.0008 -0.02

14 0.002 0.13 0.0015 0.09 0.0005 0.03

15 0.020 1.25 0.0195 1.23 0.0005 0.02

16 0.001 0.06 0.0013 0.08 -0.0003 -0.02

17 0.126 7.89 0.1250 7.88 0.0010 0.01

18 0.002 0.13 0.0022 0.14 -0.0002 -0.01

19 0.086 5.39 0.0852 5.37 0.0008 0.02

20 0.001 0.06 0.0007 0.04 0.0003 0.02

21 0.053 3.32 0.0524 3.30 0.0006 0.02

22 0.002 0.13 0.0021 0.13 -0.0001 -0.01

23 0.101 6.33 0.1004 6.33 0.0006 0.00

24 0.002 0.13 0.0016 0.10 0.0004 0.02

25 0.014 0.88 0.0143 0.90 -0.0003 -0.02

26 0.001 0.06 0.0012 0.08 -0.0002 -0.01

27 0.077 4.82 0.0770 4.86 0.0000 -0.03

28 0.002 0.13 0.0022 0.14 -0.0002 -0.01

29 0.058 3.63 0.0576 3.63 0.0004 0.00

30 0.001 0.06 0.0007 0.04 0.0003 0.02

31 0.033 2.07 0.0329 2.07 0.0001 -0.01

32 0.002 0.13 0.0020 0.13 0.0000 0.00 33 0.070 4.39 0.0701 4.42 -0.0001 -0.03

34 0.002 0.13 0.0017 0.11 0.0003 0.02

35 0.013 0.81 0.0128 0.81 0.0002 0.01

36 0.001 0.06 0.0011 0.07 -0.0001 -0.01

37 0.055 3.45 0.0547 3.45 0.0003 0.00

38 0.002 0.13 0.0022 0.14 -0.0002 -0.01

39 0.045 2.82 0.0444 2.80 0.0006 0.02

40 0.001 0.06 0.0008 0.05 0.0002 0.01

Table 1

The invention has an innovative characteristic, the so-called frequency adaptiveness. The system can adapt itself to the frequency of the applied voltage. Thus, the generated current harmonics are always steady and maintain the same value.

Experimental measurements for testing the performance of the frequency adaptive operation feature have been conducted. To that end, different trademark and model power supplies have been used. This power supply can generate electrical power at the desired frequency value, at the same time applying voltage harmonics.

230 V (RMS) voltage value along with various voltage harmonics has been applied to the invention. This process has been repeated at two different standard network frequencies: 50 and 60 Hz.

As seen in Fig. 6, 230 V (RMS) voltage has been applied to the invention along with various voltage harmonics at 50 Hz base frequency. The generated current harmonics are seen in Fig. 7. Moreover, the applied voltage and the withdrawn current are also shown in Table 2 and Table 3, respectively.

Table 2

Table 3 The applied voltage and the withdrawn current when the output frequency of the power supply is changed to 60 Hz (without changing the voltage level and voltage harmonics) are shown in Fig. 8 and Fig. 9, respectively. Again, the applied voltage and the withdrawn current in this case are also shown in Table 4 and Table 5, respectively.

At this point, it will be observed that the maximum difference is approximately 0.15% when Table 3 and Table 5 are evaluated together and the change in the generated current harmonics is analyzed based on the frequency change.

Table 4

Table 5