CN103595051A - Harmonic current tracking control method for active power filter - Google Patents

Abstract

The invention provides a harmonic current tracking control method for an active power filter. The cose idea is that harmonic currents are tracked and controlled in several times. The method mainly comprises the steps that load currents are tracked and detected, the amplitude and the phase of the harmonic currents which need to be restrained and are in assigned numbers are calculated according to actual needs, a calculated value and a reference value are subjected to subtraction, the difference value is compared with modulated waves after passing through a PI regulator, a drive circuit is driven to generate PWM control signals to drive a main circuit to generate harmonic voltages in assigned times, and the purpose of restraining harmonic waves is achieved. The method can effectively restrain the harmonic currents in assigned times, and properly compensate reactive power according to requirements.

Description

A Harmonic Current Tracking Control Method for Active Power Filter

technical field

The invention relates to tracking control of harmonic currents, in particular to a tracking control method for harmonic currents of active power filters.

Background technique

With the rapid development of power electronics technology, various nonlinear loads have brought a lot of harmonic pollution to the power grid. In order to effectively improve power quality, the disadvantages of traditional passive power filters are becoming more and more prominent, and a new type of active power filter (APF) technology has emerged as the times require. In APF technology, the tracking control of harmonic current is a key point and also a difficult point.

The current mainstream control methods include triangular wave comparison and hysteresis control. The biggest advantage of the triangular wave compared to the PWM current control method is that the switch works at a fixed frequency, but the system response is limited by the stability of the current feedback and is easily affected by the load parameters. The advantage of the hysteresis control PWM method is that it has no stability problem, is simple and easy to implement, and has a fast response speed. However, its accuracy is affected by the ring width. High precision will cause the switching frequency to be too high, and the fixed ring width will cause a large change in the switching frequency. These shortcomings limit the application of the two methods in some occasions.

Perform FFT analysis on the system harmonics. Generally, the 5th, 7th, 11th and 13th harmonics are the main components of the harmonic current. After suppressing and offsetting the major harmonics, the grid waveform is close to sinusoidal, and has no effect on the work of general equipment.

Contents of the invention

Aiming at the deficiencies of the prior art, and combining the feasibility of theoretical analysis, the present invention proposes a method for tracking and controlling harmonic currents in stages, to track and control the main order harmonics in the power grid.

A method for step-by-step tracking control of harmonic currents, comprising a harmonic current detection calculation module, a PWM control module, a main circuit power module and a drive circuit. The present invention suppresses and offsets the specified order harmonic current on the premise of knowing the specified order harmonic current (amplitude A _ihm , phase θ _ihm ), that is, the present invention focuses on considering the hierarchical tracking control of the harmonic current method. And through control, adjusting the size of the output compensation voltage can realize harmonic suppression.

The harmonic current detection and calculation module is the core of the present invention, which completes the detection and calculation of the specified harmonic current amplitude and phase, and provides a basis for the PWM control module to generate PWM control waveforms. PWM control module is the key to control APF to generate compensation harmonic current. The PWM control module, the power module and the drive circuit cooperate with the harmonic current detection and calculation module to complete the tracking compensation of the harmonic current.

比较产生PWM控制信号,控制逆变器产生相应的谐波电压。其中A_ihm、θ_ihm对应于APF已发出的指定次补偿谐波电流的实时参数，

对应系统中指定次待补偿谐波电流的实时参数。The present invention analyzes from the perspective of the root harmonic voltage generated by the harmonic current, and compares the amplitude A _ihm and phase θ _ihm of the specified order harmonic current with the reference value

Comparing and generating PWM control signal, controlling the inverter to generate corresponding harmonic voltage. Among them, A _ihm and θ _ihm correspond to the real-time parameters of the specified compensation harmonic current issued by APF,

Corresponding to the real-time parameters of the specified harmonic current to be compensated in the system.

Harmonic current detection and calculation module, which is responsible for real-time tracking and sampling of load current, and according to actual needs, calculates the electrical quantity of harmonic current of specified order, including amplitude and phase.

比较；其差值在经过PI调节器后与高频三角波进行比较，经控制电路产生PWM控制信号。再由产生的PWM控制信号驱动主电路输出电压幅值和相位合适的指定次数（m次）谐波电压，以抵消该次谐波。The PWM control module compares the amplitude A _ihm and phase θ _ihm of the specified order harmonic current with the reference value respectively

Comparison; the difference is compared with the high-frequency triangular wave after passing through the PI regulator, and the PWM control signal is generated by the control circuit. Then the generated PWM control signal is used to drive the main circuit to output voltage amplitude and phase of the specified order (m order) harmonic voltage with suitable order to offset the order harmonic.

Beneficial effect:

This method can suppress harmonics of specified order according to actual needs, has certain dynamic performance and control precision, and the switching frequency of PWM controller is low. It is suitable for tracking control of various voltage-type PWM pulse width modulation converters.

Description of drawings

Fig. 1 is a system diagram of an active power filter according to an embodiment of the present invention;

Fig. 2 is a structural diagram of an active power filter according to an embodiment of the present invention;

Fig. 3 is a schematic diagram of fractional current tracking control according to an embodiment of the present invention;

Fig. 4 is a main circuit diagram of an active power filter according to an embodiment of the present invention.

_Among them, in Figure 1, e _s is the infinite power supply of the power grid; _L is the internal impedance _of the system; i _s and i _L represent the system current and load current respectively; Indicates the connection impedance grid terminal, APF terminal voltage.

分别表示负载电流中所包含的5次、7次…m次谐波幅值参考值；θ_ih5、θ_ih7…θ_ihm分别表示APF实时发出的补偿电流中5次、7次…m次电流相位；

分别表示负载电流中所包含的5次、7次…m次谐波电流相位参考值；A_vh5、A_vh7…A_vhm分别表示5次、7次…m次谐波电压幅值；θ_vh5、θ_vh7…θ_vhm分别表示5次、7次…m次谐波电压相位；分别表示基波电压、5次、7次…m次谐波电压（均为相量）。In Fig. 3, A _ih5 , A _ih7 ... A _ihm represent the current amplitudes of the 5th, 7th ... m times of the compensation current sent by the APF in real time;

Respectively represent the 5th, 7th...m harmonic amplitude reference value contained in the load current; _θih5 , _θih7 ... _θihm respectively represent the 5th, 7th...m current phase of the compensation current issued by the APF in real time ;

Respectively represent the 5th, 7th...m harmonic current phase reference value contained in the load current; A _vh5 , _{A vh7} ... A _vhm respectively represent the 5th, 7th...m harmonic voltage amplitude; θ _vh7 ... θ _vhm represent the 5th, 7th ... m harmonic voltage phase respectively; Respectively represent the fundamental wave voltage, the 5th, 7th...m harmonic voltage (all are phasors).

In Figure 4, U _S represents the infinite system power supply; Z _S represents the system impedance; E _d represents the DC side voltage of the main circuit; S ₁ -s ₆ represents the transistor, and L represents the parallel reactance.

specific embodiment

Figure 1 depicts a schematic diagram of the APF system structure.

（只含基波，即

），APF通过一个阻抗为ZL的电抗器与电网并联，设电抗器APF端电压为

（ ${\stackrel{\·}{V}}_o={\stackrel{\·}{V}}_{o1}+{\stackrel{\·}{V}}_{o5}+{\stackrel{\·}{V}}_{o7}+{\stackrel{\·}{V}}_{o11}+{\stackrel{\·}{V}}_{o13}$ ）。Let the grid voltage be

(only the fundamental wave, ie

), the APF is connected in parallel with the power grid through a reactor with an impedance of ZL, and the terminal voltage of the reactor APF is set to

( ${\stackrel{\&Center\; Dot;}{V}}_o={\stackrel{\·}{V}}_{o1}+{\stackrel{\·}{V}}_{o5}+{\stackrel{\·}{V}}_{o7}+{\stackrel{\&Center\; Dot;}{V}}_{o11}+{\stackrel{\&Center\; Dot;}{V}}_{o13}$ ).

Take the 5th harmonic current as an example

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 05</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 05</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}$

When V _o1 =V _s1 ,

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 05</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}$

At this time, the APF only provides the system with a specified number of harmonic voltage, which plays a role in harmonic suppression.

产生指定次数谐波电流，起抑制谐波作用。When V _o1 ≠ V _s1

Generate harmonic current of specified order, play a role in suppressing harmonics.

$\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}<span\; class="notranslate">\; \&NotEqual;</span>\mathrm{<span\; class="notranslate">\; 0</span>}$

This part is no longer zero, and can perform reactive power compensation to the system. Reasonable control of the positive and negative values of V ₀₁ -V _S1 can effectively compensate the system for reactive power.

From the above analysis, the 5th harmonic voltage V _o5 is the cause of the 5th harmonic current i _h5 . To suppress the 5th harmonic current, it is only necessary to generate a corresponding 5th harmonic voltage. And the 5th harmonic voltage V _o5 and the 5th harmonic current are determined by a constant (inductance impedance) in terms of quantity.

The above electrical quantities can be characterized by magnitude and phase:

i _h5 ＝A _ih5 sin(5ωt+θ _ih5 ),

In the formula

A _ih5 indicates the amplitude of the 5th harmonic current;

ω represents the fundamental angular velocity at power frequency, that is, ω=2πf;

θ _ih5 represents the phase of the 5th harmonic current.

Therefore, in the case of knowing the 5th harmonic current amplitude A _ih5 and phase θ _ih5 , the 5th harmonic voltage can be controlled and output by controlling the 5th harmonic current amplitude A _ih5 and phase θ _ih5 , so as to achieve the purpose of eliminating the specified sub-harmonic.

Figure 2 describes the specific components of APF. It includes four parts: a harmonic current detection module, a specified order harmonic current calculation module, a specified order harmonic current tracking control module and a main circuit. Among them, the harmonic current detection module is responsible for real-time tracking and detection of harmonic current; the specified order harmonic calculation module calculates the amplitude and phase of the specified order harmonic current in the total harmonic current according to user needs; harmonic current tracking The control module adopts the triangular wave comparison PWM tracking control technology to generate PWM modulation waves with the harmonic current amplitude and phase as the control objects; the main circuit structure is a three-phase bridge inverter, and the DC side uses a stable DC power supply. Under the signal, the main circuit can generate the ideal specified sub-harmonic voltage, so as to achieve the purpose of suppressing the harmonics.

Fig. 3 has described the core part of the present invention: the principle of the step-by-step tracking control method of the active power filter current. Taking the amplitude and phase of each harmonic current as the control object, by comparing the amplitude and phase of each harmonic current with the reference value, the amplitude and phase of each harmonic voltage are output after the PI regulator. The amplitude and phase of each harmonic voltage are synthesized into sine waves of different frequencies and amplitudes, and then superimposed on the fundamental voltage to obtain the required modulation wave. Then compare the wave with the triangular wave, and generate a PWM signal through the control circuit to drive the main circuit to generate a voltage .

The various techniques used to solve the problem in the present invention mainly include the following aspects:

1. Detection and calculation of harmonic current

Extracting the fundamental wave current and the amplitude and phase of each harmonic current is the premise of the present invention. After a large number of harmonics are superimposed on the fundamental wave, the waveform still changes periodically. According to the existing theory and technology, it is easy to extract the amplitude and phase of each harmonic current. For example, DSP can be used to sample the load current and perform FFT analysis. fix the problem.

2. Generation of specified order harmonic voltage

Harmonic current comes from harmonic voltage, and there is a specific quantitative relationship between harmonic voltage and harmonic current. Through the control of the harmonic current, including the control of the amplitude and phase, the output control of the harmonic voltage can be realized.

Harmonic current and voltage can be characterized by amplitude and phase respectively:

i _hm =A _ihm sin(mωt+θ _ihm );

v _hm =A _vhm sin(mωt+θ _vhm ).

In the formula

i _hm represents the mth harmonic current;

A _ihm represents the amplitude of the mth harmonic current;

ω represents the fundamental current frequency;

θ _ihm represents the phase of the m-th harmonic current;

v _hm represents the mth harmonic voltage;

A _vhm represents the amplitude of the mth harmonic voltage;

θ _vhm represents the mth harmonic voltage phase.

As shown in Figure 3, the PWM tracking control method using triangular waves is used to control the amplitude and phase of harmonic currents. Its essence is to generate PWM signals to control the main The circuit switch is turned on and off to realize the output of harmonic voltage.

Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications, substitutions and modifications can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the invention is defined by the claims and their equivalents.

Claims (4)

1. An active power filter harmonic current tracking control method, the main steps of which include: Sampling the load current of the power system, calculating the amplitude A _ihm and phase θ _ihm of the corresponding specified order harmonic current according to the demand, and extracting the fundamental voltage in the power system

According to the corresponding control strategy, the amplitude V _vhm and phase θ _vhm of the specified order harmonic voltage are obtained; According to the obtained harmonic voltage amplitude and phase information, synthesize the corresponding specified order harmonic voltage

Superimpose the fundamental wave voltage and each harmonic voltage to obtain the modulated wave

According to the modulated wave obtained, the PWM trigger pulse signal is generated by using the triangular wave comparison method to drive the main circuit, so as to realize the suppression function of the specified order harmonic. 2. according to the control method of claim 1, wherein the concrete method that specified order harmonic voltage amplitude V _vhm and phase θ _vhm obtain is as follows: The amplitude A _ihm and phase θ _ihm of each compensation harmonic current sent by the active power filter in real time are respectively compared with the amplitude of the harmonic current to be compensated by the reference value

and phase

Make a difference, the difference is input to the PI regulator, and the amplitude V _vhm and phase θ _vhm information of each specified order harmonic voltage is output. 3. The control method according to claim 1, wherein said modulation wave The generation method is as follows: Synthesize the corresponding harmonic voltage signal according to the amplitude V _vhm and phase θ _vhm information of each specified harmonic voltage

Then each harmonic voltage signal and the fundamental voltage

The modulated wave is superimposed by the adder

4. The control method according to claim 1, wherein generating a PWM trigger pulse principle: PWM pulses are generated according to the following formula: Among them, x(t) is a modulation wave, x _c (t) is a bipolar triangle wave, and Y(t) is a PWM pulse.

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