The present invention provides a device for reactive power smooth compensation in combination with single-type harmonic filtration comprising: at least a single-type filter with a variable frequency comprising: at least two parallel capacitors of equal or different capacitances, each of which capacitors is driven by pairs of two parallel reversing thyristors, and the capacitors connected in series with an impedance forming a resonant circuit for filtering harmonics; an impedance coil having power equal to capacitance of the capacitor of maximum capacitance and having its aperture controlled by a thyristor pair; a controller having a function of measuring exerting/reacting power, cos? and analyzing the harmonic spectrum to perform the resonance frequency calculation and the power adjustment of the device for compensation in combination with a single-type harmonic filtration when the load capacity changes; a protection device automatically switching off the single-type filtration-compensation device from the electrical system when the current, voltage or both increase(s) too high to protect the elements of the filtration-compensation.


The invention relates to the field of transmission and distribution of ac power. More specifically, the present invention relates to a reactive power compensation device in combination with a harmonic filter with a variable frequency energy-saving filter, Reduce power losses on the grid.


Currently, in the world, the use of electronic devices with a large capacity (non-linear), such as inverter, computer, etc. is becoming more and more popular. In many countries around the world, the use of these devices accounted for 80, 90% of electrical appliances. The use of these types of electronic devices causes distortion (high harmonic distortion) in the electrical system. Harmonics will cause resonance phenomena, voltage surges, electrical overloads, and damage to equipment in the electrical system. In addition, it causes large losses on the lines and transformers. Harmonic Harmonics, people often use harmonics filters.

Harmonic filters on the market usually have two types: passive filters (Figure 1) and active filters (Figure 2).

Passive filters are made up of passive elements such as coils and capacitors that are connected in series. Each filter element is designed with a certain resonant frequency and is then paralleled with the nonlinear load. The resonance frequency Y of the filter is usually calculated by the following formula:

Where Xc and XL are resistors of capacitors and resistances

The working principle of this device is based on Ohm’s Law. Caused in parallel with other devices in the system, at a certain harmonic (characterized by the resonance frequency y) the impedance of the filter is extremely small compared to that of the electrical system. At that time, the harmonic current (caused by the load) will run a large part through the filter to the ground, the rest will run into the electrical system. According to Circular 32/2010 / TT-BCT, the value of each harmonics should not exceed 3% of the fundamental frequency (50Hz) and the total distortion of all harmonics exceeded 6.5% in medium and low pressure. Due to the nature of the passive noise filter, this device has the ability to self-filter harmonics, the filtered harmonic ratio only depends on the ratio of the electrical resistance and the total resistance of the device. Filter (at a certain harmonics). However, this device only effectively filters a single harmonics (due to fixed resonance frequency) but less effective than other harmonics.

This device has many advantages such as:

  • Simple, inexpensive, easy to install (can be installed in multiple locations)
  • Due to the structure of the passive equipment less power consumption, the loss of this device is small (usually less than 0.5%).
  • Noise-canceling auto-tuning
  • Reactive power compensation can be coupled at the base frequency

On the contrary, it has many disadvantages, as follows:

  • Normally, non-snow devices often cause harmonics with many different levels (typically the highest 5, 7, 11, 13 amplitudes) that each passive filter only filters one frequency In most cases, filters should be placed at different frequencies, each of which filters the harmonics at a particular frequency. In some special cases when the harmonics spectrum is composed of many different types of waves, it requires the use of a lot of expensive filtering equipment and requires a great amount of space to place the equipment.
  • Due to the structure of the passive elements, at 50Hz, the filtering devices always generate reactive power into the electrical system. Normally, the load often changes its capacity, due to the inability to adjust the reactive power, these filters will overload the reactive power and can cause great expense in the electrical system.
  • Due to the limited capacitance of the capacitor, the overvoltage of the filtering device is usually limited to a maximum of 10%, overcurrent of no more than 35%. This filter only filters 70-80% of the harmonics. However, in the case of low load and reduced amplitude harmonics the 70% filtering will not produce high harmonics. This is also a disadvantage of the passive filter (due to the inability to adjust the resonant frequency).
  • Due to the need to install multiple filters in parallel, the filter itself branches also affect each other badly. In low harmonic frequencies, high frequency harmonic filters have capacitance capacitance that will continue to generate harmonics running through low frequency filters, causing overloading of the equipment. For example, we have four harmonics filters 5, 7, 11, 13. At harmonics level 5, the filters 7, 11, 13 will cause more harmonics to pass through the filter. High-level harmonics, low-impedance filters have a resistance (electric resistance) coupling, so that some harmonics running through high-order filters will be distributed. The above interaction causes the lowest level filter condition to be overloaded, the high-order filter is unloaded (load distribution is unequal).

The second type of filter is active filter. The device works on the principle of using a harmonics measuring and analyzing unit and then playing back a harmonics with the same amplitude as the harmonic phase measured in harmonic distortion. Actually this is a device that broadcasts backward harmonic to the grid. It therefore requires a set of measurements and things to do with the accuracy and speed of the reaction.

The main advantage of this device is that it eliminates harmonics over a wide band.

However, it has many disadvantages, specifically as follows:

  • This device requires very fast measurement and analysis algorithms and very high accuracy. If it is not fast enough and accurate, it will add harmonics to the electrical system as the load changes continuously (the measurement needs to be harmonized before the load changes). So it needs a set of speed and algorithms that are very complex and expensive.
  • Due to the fact that it is a broadcasting equipment, the capacity loss is very high (at least 5%).
  • With a complex, high-demand processor, the use of small capacity equipment will be costly and not feasible.
  • This device uses less reactive power compensation.
  • High equipment costs.


The purpose of the present invention is to provide a device for coupling a harmonic filter to compensate for the reactive power on the principle of passive filtering. This device can substitute the corresponding resonant frequency with the change in power of the nonlinear load thereby enhancing the harmonics filter efficiency in the electrical system. In addition, the device also has the ability to compensate the reactive power, thus significantly reducing the losses in the electrical system.

The dip device is called a reactive power compensation unit that is coupled to a harmonics filter with a single variable frequency, which includes:

Harmonic filters with varying frequencies include capacitors (1, 2, 3) of different capacitance or capacitance in parallel, each of which is controlled by two pairs of parallel reversing thyristors (21, 22, 23) to perform the two-directional function. The capacitors (1, 2, 3) are connected in series with the impedance (4) forming a resonant circuit for filtering harmonics. The resonance frequency of this filter will change when the clamshell capacitor is closed or cut in parallel.

the resistance (0) is equal to the power of the capacitor of maximum power and is made to open the angle with the thyristor pair (20) to change the reactance of the device;

the controller (6) has the function of measuring the active and reactive power, cos? and analyzing the harmonics. It performs the resonant frequency calculation and adjusts the power of the coupling device with the wave filter. Harmonized form when the capacity of load 7 changes. The current and voltage signals are transmitted to the regulator through the current converters (TI) (10) and voltage converters (TU) (9). The signals of the harmonic current of the load will be analyzed from the current transformer (8).

the protective device (5) automatically disconnects the single-phase compensator-filter from the electrical system when the current, voltage or both increases too high for the protection of the filter element;

In the same way, the compensating filter is attached in parallel with the three-phase transmission line system for filtering harmonics and reactive power compensation; and

The control system of the single-phase filter compensates for the change in the harmonic spectrum. The power of the coil will be adjusted to ensure that the device can offset the reactive power when the capacity of the load changes.

Thus, the offset device combined with the harmonic filter is a device that combines both harmonic filtering and smooth-running reactive power. The resonance frequency of this device will change when the harmonic amplitude changes. This will contribute to the better filtering of the harmonics (with a small harmonic current, the filter will be fully filtered, while the large harmonic current will only filter a large part to avoid overloading the capacitor). In addition, the amount of feedback generated by the equipment will be adjusted by using a smooth-running thyristor to control the power of the coils (smoothly adjusting the power of the filter coupler), the power compensation Resistance will help the device to operate more efficiently than existing devices.

Another advantage of the single-harmonic compensation device is that it only uses a single filter coil. This will reduce the cost of the device by approximately 2-fold and 20-40% less than the device with 3 or 4 coil resistors that cost a lot more (more than 6 times) than the capacitor.


Figure 1 shows a picture of a passive filter;

Figure 2 shows a graphical representation of the active tilter filter;

Fig. 3 is a drawing showing the coupling device with the reactive power compensation;

Figure 4 is a flowchart of the regulator that makes the equalizer;

Figure 5 is a flowchart of the regulator that makes the equalizer;

Figure 6 is a schematic diagram of a distributed power distribution system

Figure 7 is a flowchart of the system when the filter is not set

Figure 8 is a diagram of the calculation of the system when the single-offset filter is applied

Figure 9 is a diagram of a combinational filter com- pression device used for start-up from parallel wiring with a power-efficient thyristor system.

Figure 10 is a circuit diagram of a harmonics control circuit based on the principle of reactive power control priority.

Figure 11 is an algorithmic flowchart of the combiner based on the principle of prioritizing the reactive power.


The main components of the compensation device coupled to the single-mode filter are shown in Figure 3. The compensation unit coupled to the single-phase filter consists of three capacitors 1, 2, 3, of different capacitance, these capacitors are connected in series with resistance 4. Each capacitor is closed by two pairs of opposite parallel thyristors 21, 22, 23 in order to perform the function of resonant frequency control. The device incorporates additional reactive power compensation. The resistance coil 0 also has the capacity equal to the capacity of the largest capacitor Xi and is controlled by the open angle by a pair of 20 substitute thyristors replacing the power of the device.

The regulator 6 has the function of performing calculations and adjusting the power of the compensating device coupled to a single harmonics filter when the capacity of the alternating load 7 is based on the input signal from the current transformer (TI) 8-for maximum harmonic current measurement, 10 current transformer – reactive power meter and cosɸ factor for load and voltage converter (TU) 9.

Protection device 5 automatically disconnects the power supply to the compensator – filter when the current, voltage or both increases too high to protect the components of the device.

The principle block diagram of the regulator makes the single-pass filter device shown in Figure 4.

The control unit of the compensator incorporates a single harmonics filter consisting of a 5.1 measurement circuit. This circuit defines the p power, the reactive power Q, the total power s and the cosɸ coefficient, as well as the frequency and amplitude of the harmonics. Central processing unit 5.2 for processing parameters and calculations. Screen 5,4 is used to provide the necessary information and settings of the device. 5.6 keypad to change the settings and settings. Memory 5.5 helps to record the operation of the device in normal modes and fault analysis. Lamps 5.7 indicate the working status of the device and alerts. The thyristor controller 5.3 performs the pulse generators that make the thyristor switch 5.9 as required by the central processor 5.2.

The algorithm that causes the matching equipment to harmonics filter is done as shown in Figure 5.

First, in order to achieve the most effective adjustment, the controller requires the installation of the following parameters:

Uh: the upper limit of the grid voltage (if this value is exceeded, no reactive power adjustment is made because the adjustment can damage the compensation device in combination with the single harmonics filter).

ADVANTAGES: The lower limit of the grid voltage (if lower than this value, do not adjust the power to avoid damage equipment compensated).

Cos ɸl: lower limit of cos ɸ

Cos ɸh: upper limit of cos ɸ

Cosɸrated: whore put the reactive power substation end task offset.

Ql, Qci: Power of electrical resistance and capacitance of capacitors

Qmax, Qmin: Minimum and maximum power of the compensator

PL rated: the load capacity threshold starts to adjust the reactive power and filter the harmonics (when the capacity of the load is too small, it may not need to compensate or filter the harmonics).

For a certain period of time, carry out comparisons of load capacity and voltage. If you are not satisfied then finish the process. When the load condition is greater than the threshold, the voltage in the permissible range, then find the maximum harmonics and calculate the actual cosɸ of the load.

If you do not need to change the resonance frequency, the device will only compare the cosɸ value with the chord. If cosɸ is out of the allowable range, increase the angle a (when cosɸ is lower than the threshold cosɸL) or decrease the angle a (when the cosɸh is higher than the cosɸ h threshold) of the coil.

If you need to reduce the resonant frequency, the device needs to add a capacitor. However, to avoid the reactive power of the jump device, it will first increase the capacity of the device to the highest level by adjusting the angle a of the coil resistance to when a = 180 deg. Then determine the amount of angular so that at this angle, the power of the coil resistance equal to the capacity of the capacitor is about to close the grid. At the same time, it will order the closing of the capacitor and the opening of the coil resistance from 180 deg down. At this time, the resonance frequency will decrease but the switching does not cause the power jump due to the capacity of the new capacitor close and zero resistance.

The process of increasing the resonant frequency is the opposite. Reduce capacity by reducing the opening angle a = 90 deg. Then disconnect the capacitor and switch the angle to open the ammonia.

Other schools do not conduct reactive power adjustments.

Compensation coupled with a single harmonic filter is a combination of both stepping and power regulation (through the open angle of the thyristor) of the TCR-Thyristor Controlled Reactor. The capacity of the compensation device in combination with the single-wave filter is therefore more complex than that of the other compensator.

It increases the efficiency and competitiveness of the device, which can be used with variable frequency filters using a combination of starter wiring in parallel with the thyristor units as shown in Figure 9. The 24, 26, 28 are connected in parallel with the thyristorr sets 21, 22, 23. The power supply of the starter is taken from the rear of the next Thyristor. After Thyristor 21, 22, 23 select the best shutoff time, the power supply will be energized for 24, 26, 28 startup with the help of small 25, 27, 29 power Thyristor. The word will be closed based on the principle of bitterness (voltage difference is zero). After starting from the close, the Thyristor 21, 22, 23 will be separated by stopping the source of the throttle by opening the auxiliary contact of the starter. The use of Thyristor in conjunction with magnetic starter will help to avoid the cost of the Thyristor in the long run because of the very small losses. The role of power thyristor is only to select the best time to play and then be separated from the boot from long-term work.

In some cases, the value of the harmonics is small compared to the value of the resistance. At this point, the substrate reduces the price of the product and increases its competitiveness. It can use the variable frequency harmonic filter coupled with the reactive power compensation to the system that preempts the reactive power as in Figure 10. This map uses only a current measuring device (10) to measure the reactive power without using TI (8) to measure the harmonics. The control principle of this device is shown in Figure 11.

To further clarify the effect of the harmonic filter in combination with the reactive power compensation, consider the following example.

For example: Consider a 75kW power plant at a paper mill using a motor that drives power in an inverter (nonlinear device). This engine displaces the power very complex in every hour. The main harmonic are the Harmonic Levels 5, 7, 11 and 13. The power and harmonics changes of the equipment are shown in the following table.


Hour p
















1 7.7 13.4 15.4 22.2 4.4 3.2 2.0 1.7
2 4.0 10.5 11.2 16.2 3.2 2.3 1.5 1.2
3 7.6 36.8 37.6 54.3 10.9 7.8 4.9 4.2
4 4.9 30.6 31.0 44.7 8.9 6.4 4.1 3.4
5 10.4 90.3 90.9 131.2 26.2 18.7 11.9 10.1
6 6.4 11.7 13.3 19.2 3.8 2.7 1.7 1.5
7 2.8 7.9 8.4 12.1 2.4 1.7 1.1 0.9
8 2.8 5.8 6.4 9.3 1.9 1.3 0.8 0.7
9 2.1 7.2 7.5 10.8 2.2 1.5 1.0 0.8
10 8.4 23.1 24.6 35.5 7.1 5.1 3.2 2.7
11 1.7 6.2 6.5 9.3 1.9 1.3 0.8 0.7
12 9.5 49.6 50.5 72.9 14.6 10.4 6.6 5.6
13 11.7 27.0 29.4 42.4 8.5 6.1 3.9 3.3
14 1.3 6.4 6.5 9.4 1.9 1.3 0.9 0.7
15 0.2 1.8 1.8 2.6 0.5 0.4 0.2 0.2
16 1.2 12.1 12.2 17.6 3.5 2.5 1.6 1.4
17 5.7 30.1 30.7 44.3 8.9 6.3 4.0 3.4
18 2.8 7.9 8.4 12.1 2.4 1.7 1.1 0.9


With very large harmonic distortion (over 50%), this device requires a filter. We will look at three main cases:

  1. Case 1: using a 2-filtered harmonic filter whose resonant frequency is y 1 = 4.9 and y 2 = 6.8. The capacitor has a capacity of 20 + 20kvar.
  2. Case 2: Using a 2-element analog filter with a capacitor of 45 + 40kvar.

Case 3: Use of a single reactive power compensation coupling with 2 capacitors with a capacity of 70 + 15kvar.

The main calculations are as follows:

Short circuit of INM power system = 14kA

110 / 22kV transformer: power Sdml = 40MVA, short circuit power loss ΔPN1= 175kW, short circuit voltage loss ΔU m = 10.5%

Aluminum cable line: 5km long with output resistance = 0.325Q / km, x0 = 0.107Ω/km length of cable L = 5km

Transformers 22 / 0,4kY: power Sdm2 = 1000kVA, ΔPN2 = 12kw, ΔU = 4.5%

With the above information, the equivalent impedance of the entire system will be

is Rtđ = Rht + RTl + RC + RT2 = 0.001926 Ω

Equivalent resistance of the system Xtđ = 0.0098Q

The parameters of the filter are calculated as follows:

  1. In cases 1 and 2: the equipment consists of two parallel hooks, we know the capacity of the capacitor, the capacitance of the capacitor is calculated according to the formula:

The resistance of the inductance is calculated by the resonant frequency and the impedance of the capacitor according to the formula


At each of the different harmonics, the impedance of the capacitor and the electrical resistance are changed, the impedance of a branch of the filter is given by the formula:


The resistance of both filter arms at each harmonics will be:


Harmonic currents entering the electrical system will follow the Ohm law for two parallel branches:


We will in turn calculate the two heads with 4 main types of harmonics h = 5, 7, 11, 13.

  1. Case 3: Compensation device combined with filter with only one filtered eye is the XL reactance, when the capacity of the load is small, we just plug the capacitor Xci into the electrical system, then the resonant frequency of device y = 5, the value of the impedance


When the load increases, we add the XC2 capacitor, then 2 capacitors Xci and

XC2 parallel, the value of the resistance


As a result, the resonant frequency of the compensator-filter will decrease according to the formula

Reducing the resonant frequency avoids the overloading of the capacitor, making the device work for a long time.

Because the filter compensator uses a thyristor that makes the coil winding, the coil windings produce a harmonics wave. We will get the largest harmonic values on the substrate calculator using the refit device.












9.9 3.5 1.7 0.7 0.5

Calculated results of using the equipment are given in the table below:


Capacity (kvar)

Loss due to reactive power (kWh)

Harmonic losses (kWh)

Total Loss (kWh)

Ratio (%)

Fixed Filtration Device 1






Compensation equipment combined with filtration






Fixed filter equipment 2






It can be seen that the compensation device combined with the harmonic filter has the best effect when the power loss is only 19.3% compared with the fixed filter 40kvar capacity. The option of using a fixed filter with a capacity of 85kvar is the worst option with 5 times higher cost than 40kvar and 26 times less than using a filter.

Thus, it can be seen that at comparable costs, the harmonics filter compensation device is much more effective than the harmonic filter with constant power (no induction).


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