RU2512886C1 - Device to compensate high harmonics and correct grid power ratio - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device comprises an inverter, an accumulating capacitor, an output smoothening passive filter, and a control system controller, at the same time the control system controller is equipped with a grid current sensor, voltage sensor, pulse shaper on the basis of relay controllers with variable width of hysteresis, phase converters of current and voltage, a unit of phase synchronisation and a controller of accumulating capacitor voltage, control drivers for inverter power-circuit keys; the device is equipped with grid current phase converter, reference current phase converter and voltage-shaping unit.

EFFECT: reducing coefficient of distortion for sinusoidal current curves and line voltage in presence of non-linear load which mode is connected to dynamic change of consumed non-sinusoidal current; increasing power factor of the grid as per the main component.

1 dwg

Description

The invention relates to electrical engineering and the electric power industry, and in particular to devices for suppressing and compensating for higher harmonics in electric networks and correcting power factor. The device can be used in power supply systems of industrial enterprises with a large amount of non-linear load.

Known active filter (JP patent No. 6091711, etc. pr. 04.03.1988) containing an inverter, a storage capacitor, computing circuits and a memory unit. The output current of the active filter is adjusted depending on the regulatory value of the current, which is used as the high-frequency component of the current of the nonlinear load. The active filter in this device contains computational circuits that determine the difference between the regulating current value and the output current of the filter, and a memory unit, the input of which receives the output signal of the circuits, where at least part of the period of the regulating current value is recorded. In self-learning control circuits, the time moments following the delay intervals, for example, equal to one period of the current control value, are taken as the reference ones. Computational circuits generate a signal for adjusting the current regulating value as a result of reading the contents of the memory block ahead of the reference time points by a certain interval equal to the delay time of the filter output current.

The disadvantage of this device is the impossibility of phase synchronization of the voltage and current of the compensated network, and the mechanism for suppressing higher harmonics is based on the adjustment of the regulating current during the delay time of the filter, which in the conditions of the dynamic change of the current of the nonlinear load will not allow fixing and working out sudden surges of the network current. The device lacks a voltage regulator for the storage capacitor to control the magnitude of the compensation current and to work out sudden changes in the current of the compensated load. The device does not allow the inverter of the active filter to work with a variable frequency PWM.

A control device for an active filter (JP patent No. 6055009, etc. pr. 11/16/1987) containing a phase synchronization unit, computational circuits, a storage capacitor and an inverter is known. The phase synchronization unit generates phase signals synchronously with the voltage of the source, which are processed by computer circuits. As a result, high-frequency current signals are generated, which are the difference between the main harmonic current signals and the load current measurement signals, which are used as reference signals when regulating the active filter's output current using PWM.

The disadvantage of this device is the lack of a voltage regulator for the storage capacitor and that the inverter in the device operates with a constant PWM frequency.

Known active filter of higher harmonic components of the currents and the power factor correction device, (US patent No. 5977660, etc. pr 08.08.1997) containing an inverter, controller, storage capacitors and output passive smoothing filter. The controller performs the current prediction procedure for the next period of time in order to reduce the phase difference created by the load between the current and the mains voltage. The control procedure integrates the difference between the real currents in the line and their required values at equivalent time intervals on various alternating current cycles of the fundamental frequency. Integral values can be combined with proportionally adjustable differential currents to reduce or completely compensate for harmonic currents. The current balancing procedure allows the active filter to equalize currents in multiphase power lines. All these procedures can be used both individually and together.

The disadvantage of the filter is the inverter's inability to work with a variable PWM frequency.

A device for compensating higher harmonics and correcting the power factor of a network is adopted, which is adopted as a prototype (patent RU No. 2446536, etc. pr. 30.11.2010), comprising an inverter, a storage capacitor, an output smoothing passive filter and a control system controller, while the control system controller is equipped with filter current sensor, network current sensor, voltage sensor, pulse generator based on relay controllers with variable hysteresis width, phase current and voltage converters, phase synchronization unit and Knob storage capacitor voltage.

The disadvantage of the prototype is the lack of compensation for the reactive power of the main component (first harmonic). The prototype is effective in compensating for the reactive power that only higher harmonics create.

The technical result of the invention is to reduce the distortion coefficients of the sinusoidal shape of the curves of the current and voltage of the network in the presence of a non-linear load, the mode of operation of which is associated with a dynamic change in the consumed non-sinusoidal current, and increase the power factor of the network along the main component. The proposed device can be in demand in enterprise networks, where non-linear load in the form of various types of frequency converters of variable-speed drive systems of technological installations and complexes has become widespread.

The technical result of the invention is achieved by the fact that the device for compensation of higher harmonics and correction of the power factor of the network containing an inverter, a storage capacitor, an output smoothing passive filter and a controller of the control system, while the controller of the control system is equipped with a current sensor of the network, voltage sensor, pulse shaper on basis of relay controllers with variable hysteresis width, phase current and voltage converters, phase synchronization unit, voltage regulator the storage capacitor, and the input of the current sensor is connected to the terminals of the supply network, the input of the voltage sensor is connected to the terminals of the supply network, the output of the storage capacitor voltage regulator is connected to the inputs of the inverter power switch drivers, the input of the storage capacitor voltage regulator is connected to the terminals of the storage capacitor, output the network current sensor is connected to the input of the storage capacitor voltage regulator, the output of the voltage sensor is connected to the phase voltage converter, the output of the phase voltage converter is connected to the input of the phase synchronization unit, the output of the pulse generator is connected to the inputs of the inverter power switch drivers, the output of the phase current converter and the output of the storage capacitor voltage regulator are connected to the input of the pulse generator, the phase converter of network currents, phase converter are turned on reference currents and a voltage generation unit, while the output of the phase synchronization unit is connected to the input of a new reference current converter, the output of which is connected to the input of the voltage generation unit, the output of which is connected to the input of the phase current converter, the output of the phase synchronization unit is connected to the input of the voltage generation unit, the output of the network current sensor is connected to the input of the phase current converter, the output of which is connected to the input of the phase converter of the reference currents, the output of the voltage regulator of the storage capacitor is connected to the input of the voltage generation unit.

The proposed device is illustrated in figure 1, which shows the structure of the device. In Fig.1: 1 - nonlinear load; 2 - inverter; 3 - storage capacitor; 4 - output passive filter; 5 - voltage sensor; 6 - phase voltage converter; 7 - phase synchronization block; 8 - phase current converter; 9 - pulse shaper; 10 - network current sensor; 11 - voltage regulator of the storage capacitor; 12 - controller control system; 13 - phase converter of network currents; 14 - phase converter of the reference currents; 15 - block forming stresses.

The device for the compensation of higher harmonics and correction of the power factor of the network operates as follows. A storage capacitor 3 is connected to the inverter 2, an output passive filter 4 is connected to the inverter 2 output. The control system controller 12 controls the voltage of the storage capacitor 3 and generates control pulses of the power keys of the inverter 2. The control system controller 12, in turn, consists of a voltage sensor 5, phase voltage converter 6, phase synchronization unit 7, phase current converter 8, pulse shaper 9, current sensor network 10, voltage regulator drive th capacitor 11, phase currents of the inverter network 13, phase converter 14, the reference currents, voltages forming unit 15.

The input of the current sensor of network 10 is connected to the terminals of the supply network, the input of the voltage sensor 5 is connected to the terminals of the supply network, the output of the voltage regulator of the storage capacitor 11 is connected to the inputs of the drivers for controlling the power keys of the inverter 2, the input of the voltage regulator of the storage capacitor 11 is connected to the terminals of the storage capacitor 3, the output of the current sensor of the network 10 is connected to the input of the pulse former 9, the output of the current sensor of the network 10 is connected to the input of the voltage regulator of the storage capacitor 11, the output of the sensor to voltage 5 is connected to the input of the phase voltage converter 6, the output of the phase voltage converter 6 is connected to the input of the phase synchronization unit 7, the output of the phase synchronization unit 7 is connected to the input of the phase converter of the reference currents 14, the output of which is connected to the input of the voltage generation unit 15, the output of which is connected with the input of the phase current converter 8, the output of the voltage regulator of the storage capacitor 11 is connected to the input of the phase current converter 8, the output of the phase current converter 8 and the output the voltage regulator of the storage capacitor 11 is connected to the input of the pulse shaper 9, the output of which is connected to the inputs of the drivers for controlling the power keys of the inverter 2, the output of the current sensor of the network 10 is connected to the input of the phase converter of the network currents 13, the output of which is connected to the input of the phase converter of the reference currents 14, output phase synchronization unit 7 is connected to the input of the voltage generation unit 15.

The proposed device differs from the prototype in the presence of a phase converter of the network currents 13, a phase converter of the reference currents 14, a voltage generation unit 15, the absence of a sensor for the actual filter current, the absence of communication between the phase converter 8 and the voltage regulator of the storage capacitor 11, the absence of communication between the current sensor of the network 10 and pulse shaper 9, the lack of comparison of the actual inverter current, mains current and the current task of the voltage regulator of the storage capacitor 11, from the absence of communication between the filter current sensor (in the prototype, position 12 of figure 1) with the pulse shaper 9.

The measuring signals of the linear voltage of the distorted network from the voltage sensor 5 are fed to the input of the phase voltage converter 6, which processes the incoming signals in accordance with the following expressions:

u _α = (2 u _ab + u _bc ) / 3,

, $$u_{\beta }=u_{bc}/\sqrt{3}$$

,

where u _ab , u _bc are the measured linear voltages of the distorted network; u _α , u _β are the transformed linear voltages of the distorted network in the coordinate system αβ0. Phase transformations make it possible to determine the angle φ between the image vector of the distorted network voltage and its projection onto the α axis. The nature of the change and the angle φ contain information about the level of distortion, the higher harmonics present and the phase shift of the voltage and current of the compensated network.

The output signals u _α , u _{β of the} phase voltage converter 6 are fed to the input of the phase synchronization unit 7, which adjusts the direction cosines and sines of the angle φ so that the resulting value φ ′ corresponds to the sinusoidal shape of the network voltage curves. The initial guide cosines and sines are defined as follows:

cosφ = u _α / u _sm ;

sinφ = u _β / u _sm ; (2)

$$u_{sm}=\sqrt{u_{\alpha }^2+u_{\beta }^2.}$$

Further, the obtained values of cosφ and sinφ are adjusted by the phase synchronization unit 7 to the values cosφ ′ and sinφ ′ corresponding to the sinusoidal shape of the network voltage curves.

The measuring signals of the phase currents of the compensated network i _a , i _b , i _c from the current sensor of the network 10 are fed to the input of the phase converter of the network currents 13, which processes the incoming signals in accordance with the following expressions:

$$i_{\alpha }=\frac{2}{3}\cdot i_a-\frac{\mathrm{one}}{3}\left(i_b+i_c\right);$$

$$i_{\beta }=\frac{\sqrt{3}}{3}\left(i_b-i_c\right),(2)$$

After that, the output signals cosφ ′ and sinφ ′ of the phase synchronization unit 7 and the output signals i _α and i _{β of the} phase converter of the network currents 13 are input to the phase converter of the reference currents 14, which processes the input signals in accordance with the following expressions:

i _d = i _α cosφ ′ + i _β sinφ ′;

i _q = i _β cosφ′-i _α sinφ ′. (3)

Next, the output signals i _d and i _{q of the} phase converter of the reference currents 14 together with the output signal of the current reference i _s from the controller 11 and the output signals cosφ ′ and sinφ ′ of the phase synchronization unit 7 are fed to the input of the voltage generation unit 15, which processes the input signals in accordance with the following expressions:

u _α = (- K ₁ · (i _s -i _d ) / ΔT + ω _k · L _d · i _q + U _m ) cosφ ′ - (K ₂ i _q / ΔT-ω _k · L _d · i _d ) sinφ ′;

u _β = (- K ₁ · (i _s -i _d ) / ΔT + ω _k · L _d · i _q + U _m ) sinφ ′ + (K ₂ i _q / ΔT-ω _k · L _d · i _d ) cosφ ′, (4)

where K ₁ , K ₂ , ΔT, L _d , ω _k , U _m are the parameters of the voltage generating unit 15, the values of which are determined depending on the parameters of the compensated network.

After that, the output signals of the voltage generating unit 15 u _α and u _β are fed to the input of the phase current transformer 8, which processes the input signals in accordance with the following expressions:

u _a = u _α ;

$$u_b=\left(\sqrt{3}\cdot u_{\beta }-u_{\alpha }\right)/2;(5)$$

. $$u_c=\left(-\sqrt{3}\cdot u_{\beta }-u_{\alpha }\right)/2$$

.

Next, the output signals u _a , u _b , u _{c of the} phase current converter 8 together with the current reference signal from the controller 11 i _s are fed to the input of the pulse shaper 9, made on the basis of relay controllers.

The controller 11 also controls the voltage level of the storage capacitor 3 at a given value and gives a signal to the power switches of the inverter 2 to recharge the capacitor 3 if the actual voltage is lower than the reference. Comparing the set and actual values of the voltage of the storage capacitor 3, taking into account the magnitude of the distorted current of the network from the sensor 10, the controller 11 generates a reference signal for the charge current i _s for the inverter. The controller 11, having high speed, which allows you to process sudden changes in the current of a nonlinear load lasting from units to tens of microseconds, provides a margin of the voltage of the capacitor 3 in the event of a sudden change in the operating mode of the nonlinear load, which leads to an increase in the distorted current consumed by it and, as a result, increase in the value of the required compensation current. The controller 11 has upper and lower limits, which do not allow the device to operate in continuous overload mode.

Changing the width and frequency of the hysteresis of the relay controllers of the pulse shaper in the proposed device allows us to provide the operating mode of the inverter with a variable PWM frequency, the required accuracy of working out the task for the compensation current while maintaining a speed level sufficient to track dynamic changes in the operating mode of most types of non-linear loads, and to monitor continuous spectrum change generated compensation current.

With an increase in the hysteresis frequency of relay controllers, the accuracy of working out the task for the inverter compensation current increases. The hysteresis width of the relay controllers Δi determines the frequency of the PWM inverter.

The dynamic change in the operating mode of the compensated non-linear load and the harmonic spectrum generated by it makes it inefficient to use other types of controllers to generate control pulses of the inverter keys in this method.

The presence of the phase converter of the network currents 13, the phase converter of the reference currents 14 and the voltage generation unit 15 allows for the correction of the power factor of the network according to the main component.

The hardware implementation of the proposed device can be carried out using existing power electrical, electronic and microprocessor devices with proper selection and configuration of the relevant parameters.

Claims (1)

A device for compensating higher harmonics and correcting the power factor of the network, containing an inverter, a storage capacitor, an output smoothing passive filter and a controller of the control system, while the controller of the control system is equipped with a network current sensor, voltage sensor, pulse shaper based on relay controllers with variable hysteresis width, phase current and voltage converters, phase synchronization unit, voltage regulator of the storage capacitor, and the input of the network current sensor connected to the terminals of the supply network, the input of the voltage sensor is connected to the terminals of the supply network, the output of the storage capacitor voltage regulator is connected to the inputs of the inverter power switch drivers, the input of the storage capacitor voltage regulator is connected to the terminals of the storage capacitor, the output of the network current sensor is connected to the input of the storage voltage regulator capacitor, the output of the voltage sensor is connected to the input of the phase voltage converter, the output of the phase voltage converter the connection is connected to the input of the phase synchronization unit, the output of the pulse shaper is connected to the inputs of the inverter power switch drivers, the output of the phase current converter and the output of the storage capacitor voltage regulator are connected to the input of the pulse shaper, characterized in that it is equipped with a phase converter of network currents, a phase reference converter currents and a voltage generation unit, while the output of the phase synchronization unit is connected to the input of the phase converter of the reference currents c, the output of which is connected to the input of the voltage generation unit, the output of which is connected to the input of the phase current converter, the output of the phase synchronization unit is connected to the input of the voltage generation unit, the output of the network current sensor is connected to the input of the phase current converter, the output of which is connected to the input of the phase converter reference currents, the output of the storage capacitor voltage regulator is connected to the input of the voltage generation unit.