CN104993495B - Suitable for the Active Power Filter-APF Direct Current Control method under weak grid conditions - Google Patents

Abstract

The invention discloses suitable for the Active Power Filter-APF Direct Current Control method under weak grid conditions, according to following implementation：Step 1, gathers the instantaneous value of the electric current that voltage at weak network system PCC points, DC side voltage of converter, the instantaneous value of load current, and inverter send；It is input in dsp processor after the conditioned processing of circuit of current instantaneous value that step 2, the instantaneous value that will be gathered, and inverter send, is converted to data signal；Step 3, dsp processor is processed by data signal, obtains the instruction current signal of Active Power Filter-APF；Instruction current signal and data signal are carried out stagnant ring and compared by step 4, dsp processor, and control DSP to send PWM ripples；Step 5, the PWM ripples that will be sent are sent to the drive circuit of the IGBT module of inverter, and control inverter is according to instruction current signal.The present invention idle harmonic electric current that effectively accurate compensation is loaded.

Description

Suitable for the Active Power Filter-APF Direct Current Control method under weak grid conditions

Technical field

The invention belongs to electric and electronic technical field, it is related to the Active Power Filter-APF being applied under weak grid conditions direct Current control method.

Background technology

As fossil energy is increasingly deficient, environmental problem is increasingly serious, and the regenerative resource of cleaning is obtained more and more Pay attention to.Therefore distributed generation system as regenerative resource one of main application mode, the ratio in power network is constantly carried It is high.According to electric network composition, the impedance of power network is mainly determined by the converter of low-power and distribution line impedance.Distributed power source Increase and cause power network under different service conditions, impedance be can not ignore and be changed in a scope wider, and power network is presented Go out light current net characteristic.The extensive use of power electronic equipment simultaneously can bring increasingly serious electric energy to pollute to power network, generally should Administered with Active Power Filter-APF (Active Power Filter are APF).And for light current net, due to common tie point (Point of Common Coupling are PCC) voltage contains and flows through background harmonicses caused by electric network impedance by harmonic current, Therefore PCC voltages are usually expressed as distortion imbalance.Therefore the improvement of the quality of power supply is carried out, it is necessary to solve using APF in light current net Problem certainly is：When APF can be uneven in PCC voltage distortions and frequency deviation occurs, harmonic wave and idle electricity are real-time and accurately detected Flow and compensate.

For the real-time detection of harmonic and reactive currents, most widely used at present is instantaneous reactive power theory (Instantaneous Reactive Power Theory are IRP Theory) and its extended method and synchronous coordinate system method (Synchronous Reference Frame are SRF Method).But it is uneven that IRP theories are not suitable for PCC voltage distortions The state of weighing apparatus.Although the extended method of IRP and SRF methods are not influenceed by voltage distortion or non-equilibrium state, need to detect positive sequence The real-time phase of fundamental voltage.The uneven real-time phase to detection positive sequence fundamental voltage of distortion of PCC voltages brings larger Difficulty.Although Phase Lock Technique relatively advanced at present can to a certain extent meet above-mentioned condition, they are implemented Mostly more complicated and to have certain delay, it is necessary to accurate parameter designing, these are all unfavorable for the reality in engineering Using.

Another main direction of studying that compensation dynamic is APF is improved by eliminating detection time delay.Using self adaptation Nonlinear Control eliminates influence of the system detectio time delay to compensation effect.Disappear by the way of repetitive controller is corrected automatically Except the influence of time delay, but its dynamic responding speed is slower, it is impossible to compensation is met when system power fluctuates and is required.Patrolled using fuzzy The intelligent algorithms such as controller, synovial membrane controller are collected to be predicted control to eliminate the influence of detection time delay.Although the above method has Influence of the time delay for compensation effect is eliminated to effect, but is implemented complex.

The content of the invention

Object of the present invention is to provide suitable for the Active Power Filter-APF Direct Current Control under weak grid conditions Method, solves the problems, such as that traditional Direct Current Control cannot accurate compensation harmonic wave and reactive power under weak grid conditions.

The technical solution adopted in the present invention is, it is adaptable to the Active Power Filter-APF Direct Current control under weak grid conditions Method processed, implements according to following steps：

Step 1, gathers voltage e at weak network system PCC points_a、e_bAnd e_cInstantaneous value, DC side voltage of converter v_dc's Instantaneous value, load current i_La、i_LbAnd i_LcInstantaneous value, and the electric current i that inverter sends_ca、i_cbAnd i_ccInstantaneous value；

Step 2, the e that will be collected_a、e_b、e_c、v_dc、i_La、i_LbAnd i_LcInstantaneous value, and the electric current that inverter sends i_ca、i_cbAnd i_ccInstantaneous value is converted to data signal in being input to dsp processor after modulate circuit treatment by A/D modules e_a、e_b、e_c、v_dc、i_La、i_Lb、i_Lc、i_ca、i_cbAnd i_cc；

Step 3, dsp processor is by data signal e_a、e_b、e_c、v_dc、i_La、i_LbAnd i_LcProcessed, obtained active electrical The instruction current signal i of force filter_refa、i_refb、i_refc；

Step 4, dsp processor is by instruction current signal i_refa、i_refb、i_refcWith data signal i_ca、i_cbAnd i_ccCarry out stagnant Ring compares, and controls the PWM module of DSP to send PWM ripples；

Step 5, the PWM ripples that dsp processor is sent are sent to the drive circuit of the IGBT module of inverter, control inversion Device is according to instruction current signal i_refa、i_refb、i_refcSend electric current, according to the harmonic wave that sends in the weak network system of current compensation and Reactive power.

The features of the present invention is also resided in,

The instruction current signal that Active Power Filter-APF is obtained in step 3 is specifically implemented according to following steps：

1) instantaneous value of system PCC point voltages and load current is respectively：

In formula (1), (2)：M, n are overtone order ,+positive sequence is represented ,-represent negative phase-sequence；ω is angular speed, and t is the time,It is positive sequence m subharmonic voltage amplitudes,It is negative phase-sequence m subharmonic voltage amplitudes,It is initial for negative phase-sequence m subharmonic voltages Phase angle,It is the initial phase angle of positive sequence m subharmonic voltages,It is positive sequence nth harmonic current amplitude,It is negative phase-sequence nth harmonic Current amplitude,It is the initial phase angle of negative phase-sequence nth harmonic electric current,It is the initial phase angle of positive sequence nth harmonic electric current；

2) voltage and load current instantaneous value of PCC points are converted into two-phase rest frame；

Coordinate value of the voltage of PCC points in two-phase rest frame be：

In formula (3), (4)：

3) voltage vector, electric current arrow are converted to according to the locus between two-phase rest frame and rotating coordinate system The coordinate value that amount is fastened in rotational coordinates；

Voltage vector is in the coordinate value that rotational coordinates is fastened：

In formula (5),γ is the initial phase angle of xy coordinate systems；

Current phasor is in the coordinate value that rotational coordinates is fastened：

4) coordinate value that voltage vector is fastened in rotational coordinates is extracted using low pass filter, obtains PCC point voltages and bear Carry current first harmonics positive-sequence component is in the coordinate value that rotational coordinates is fastened：

In formula (7),It is fundamental positive sequence voltage, the amplitude of electric current,It is fundamental positive sequence voltage, electricity The initial phase angle of stream, γ is the initial phase angle of xy coordinate systems；

5) according to 3) and 4) voltage, the fundamental positive sequence of electric current obtained in fundamental positive sequence voltage same rotating speed in the same direction The coordinate value fastened of rotational coordinates, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is

Definition further according to watt current obtains watt current, and expression is as follows：

In formula (8),

Then watt current is in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage：

6) according to DC voltage and the deviation of desired value, the watt current needed for obtaining voltage control using PI controllers i_pdc3) and 4), further according to the coordinate value that the PCC point voltage fundamental positive-sequence components obtained in are fastened in rotational coordinates, by i_pdcAlso throw To xy coordinate systems, its coordinate value is respectively shadow：

By i_pdcComponent on xy coordinate systems is added separately to load component of the watt current on xy axial coordinates, then be Unite consumption watt current be in the coordinate value of xy coordinate systems：

7) watt current is entered into row matrix in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage The three-phase instantaneous value that inverse transformation obtains watt current is respectively：

In formula (12),γ is first for xy coordinate systems Phase angle；

8) the three-phase instantaneous value of the system watt current for 7) obtaining is subtracted with the load current three-phase instantaneous value for collecting, i.e., The instruction current signal of Active Power Filter-APF is obtained,

When PCC electric voltage frequencies are displaced to ω ' by ω, the instruction current signal of Active Power Filter-APF is obtained in step 3 Specifically implement according to following steps：

1) instantaneous value of system PCC point voltages and load current is respectively：

In formula (14), (15), m, n are overtone order ,+positive sequence is represented ,-represent negative phase-sequence；ω₀It is angular speed, when t is Between,It is positive sequence m subharmonic voltage amplitudes,It is negative phase-sequence m subharmonic voltage amplitudes,At the beginning of negative phase-sequence m subharmonic voltages Beginning phase angle,It is the initial phase angle of positive sequence m subharmonic voltages,It is positive sequence nth harmonic current amplitude,For negative phase-sequence n times is humorous Ripple current amplitude,It is the initial phase angle of negative phase-sequence nth harmonic electric current,It is the initial phase angle of positive sequence nth harmonic electric current；

2) voltage and load current instantaneous value of PCC points are converted into two-phase rest frame；

Coordinate value of the voltage of PCC points in two-phase rest frame be：

In formula (16), (17),

3) voltage vector, electric current arrow are converted to according to the locus between two-phase rest frame and rotating coordinate system The coordinate value that amount is fastened in rotational coordinates；

Voltage vector is in the coordinate value that rotational coordinates is fastened：

In formula (18),γ is the first angle of xy coordinate systems；

Current phasor is in the coordinate value that rotational coordinates is fastened：

4) coordinate value that voltage vector is fastened in rotational coordinates is extracted using low pass filter, obtains PCC point voltages and bear Carry current first harmonics positive-sequence component is in the coordinate value that rotational coordinates is fastened：

In formula (20),It is fundamental positive sequence voltage, the amplitude of electric current,It is fundamental positive sequence voltage, electricity The initial phase angle of stream, γ is the initial phase angle of xy coordinate systems；

5) according to 3) and 4) voltage, the fundamental positive sequence of electric current obtained in fundamental positive sequence voltage same rotating speed in the same direction The coordinate value fastened of rotational coordinates, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is

Further according to the definition of watt current, to obtain watt current expression formula as follows：

In formula (21),

Then watt current is in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage：

6) according to DC voltage and the deviation of desired value, the watt current needed for obtaining voltage control using PI controllers i_pdc, further according to the coordinate value that the PCC point voltage fundamental positive-sequence components obtained in step 3.4 are fastened in rotational coordinates, by i_pdc Xy coordinate systems are projected to, its coordinate value is respectively：

By i_pdcComponent on xy coordinate systems is added separately to load component of the watt current on xy axial coordinates, then be Unite consumption watt current be in the coordinate value of xy coordinate systems：

7) watt current is entered into row matrix in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage The three-phase instantaneous value that inverse transformation obtains watt current is respectively：

In formula (25),γ is first for xy coordinate systems Phase angle；

8) the three-phase instantaneous value of the system watt current obtained in being subtracted 7) with the load current three-phase instantaneous value for collecting, The instruction current signal of Active Power Filter-APF is obtained final product,

The beneficial effects of the invention are as follows：The present invention is suitable for the Active Power Filter-APF Direct Current control under weak grid conditions Method processed, can complete dynamic tracing compensation within an electric cycle, and dynamic response characteristic is good.There is no frequency deviation by weak line voltage Influence.When weak network system is in stable state, APF can effectively accurate compensation load idle harmonic electric current, whole control Phaselocked loop need not be used during system, detection time delay is significantly reduced, it is ensured that the dynamic of APF compensation.

Brief description of the drawings

Fig. 1 is APF master Active Power Filter-APF Direct Current Control method of the present invention under weak grid conditions Circuit topological structure figure；

Fig. 2 is Active Power Filter-APF Direct Current Control method and step 3 of the present invention under weak grid conditions Two-phase rest frame to and two-phase xy rotating coordinate systems；

Fig. 3 is the APF Active Power Filter-APF Direct Current Control method of the present invention under weak grid conditions Control strategy block diagram；

Fig. 4 is the simulation waveform of weak network system PCC points voltage；

Fig. 5 is the simulation waveform of light current net system load electric current；

Fig. 6 is the simulation waveform of system A phases PCC point voltages and light current net system power before compensation；

Fig. 7 is the simulation waveform of system A phases PCC point voltages and light current net system power after compensation；

Fig. 8 is the fft analysis of system A phases PCC point voltages and light current net system power before compensation；

Fig. 9 is the fft analysis of system A phases PCC point voltages and light current net system power after compensation；

Figure 10 is the simulation waveform of load current when the system load of light current net is mutated；

Figure 11 is the simulation waveform of inverter current trace command electric current when the system load of light current net is mutated；

Figure 12 is the system A phases PCC point voltages and light current net system power after compensation when the system load of light current net is mutated Simulation waveform；

Figure 13 is that system A phases PCC point voltages and weak network system that weak network system occurs during+5Hz frequency deviations after compensation are electric The simulation waveform of stream；

Figure 14 is that system A phases PCC point voltages and weak network system that weak network system occurs during -5Hz frequency deviations after compensation are electric The fft analysis of stream；

Figure 15 is that system A phases PCC point voltages and weak network system that weak network system occurs during+5Hz frequency deviations after compensation are electric The simulation waveform of stream；

Figure 16 is that system A phases PCC point voltages and weak network system that weak network system occurs during -5Hz frequency deviations after compensation are electric The fft analysis of stream.

Specific embodiment

The present invention is described in detail with reference to the accompanying drawings and detailed description.

The invention provides suitable for the Active Power Filter-APF Direct Current Control method under weak grid conditions, according to Lower step is implemented：

Step 1, gathers voltage e at weak network system PCC points_a、e_bAnd e_cInstantaneous value, DC side voltage of converter v_dc's Instantaneous value, load current i_La、i_LbAnd i_LcInstantaneous value, and the electric current i that inverter sends_ca、i_cbAnd i_ccInstantaneous value；

Step 2, the e that will be collected_a、e_b、e_c、v_dc、i_La、i_LbAnd i_LcInstantaneous value, and the electric current that inverter sends i_ca、i_cbAnd i_ccInstantaneous value is converted to data signal in being input to dsp processor after modulate circuit treatment by A/D modules e_a、e_b、e_c、v_dc、i_La、i_Lb、i_Lc、i_ca、i_cbAnd i_cc；

Step 3, dsp processor is by data signal e_a、e_b、e_c、v_dc、i_La、i_LbAnd i_LcProcessed, obtained active electrical The instruction current signal i of force filter_refa、i_refb、i_refc；

The instruction current signal that Active Power Filter-APF is obtained in step 3 is specifically implemented according to following steps：

1) instantaneous value of system PCC point voltages and load current is respectively：

In formula (1), (2)：M, n are overtone order ,+positive sequence is represented ,-represent negative phase-sequence；ω is angular speed, and t is the time,It is positive sequence m subharmonic voltage amplitudes,It is negative phase-sequence m subharmonic voltage amplitudes,It is initial for negative phase-sequence m subharmonic voltages Phase angle,It is the initial phase angle of positive sequence m subharmonic voltages,It is positive sequence nth harmonic current amplitude,It is negative phase-sequence nth harmonic Current amplitude,It is the initial phase angle of negative phase-sequence nth harmonic electric current,It is the initial phase angle of positive sequence nth harmonic electric current；

2) voltage and load current instantaneous value of PCC points are converted into two-phase rest frame；

Coordinate value of the voltage of PCC points in two-phase rest frame be：

In formula (3), (4)：

3) voltage vector, electric current arrow are converted to according to the locus between two-phase rest frame and rotating coordinate system The coordinate value that amount is fastened in rotational coordinates；

Voltage vector is in the coordinate value that rotational coordinates is fastened：

In formula (5),γ is the initial phase angle of xy coordinate systems；

Current phasor is in the coordinate value that rotational coordinates is fastened：

4) coordinate value that voltage vector is fastened in rotational coordinates is extracted using low pass filter, obtains PCC point voltages and bear Carry current first harmonics positive-sequence component is in the coordinate value that rotational coordinates is fastened：

In formula (7),It is fundamental positive sequence voltage, the amplitude of electric current,It is fundamental positive sequence voltage, electricity The initial phase angle of stream, γ is the initial phase angle of xy coordinate systems；

5) according to 3) and 4) voltage, the fundamental positive sequence of electric current obtained in fundamental positive sequence voltage same rotating speed in the same direction The coordinate value fastened of rotational coordinates, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is

Definition further according to watt current obtains watt current, and expression is as follows：

In formula (8),

Then watt current is in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage：

6) according to DC voltage and the deviation of desired value, the watt current needed for obtaining voltage control using PI controllers i_pdc3) and 4), further according to the coordinate value that the PCC point voltage fundamental positive-sequence components obtained in are fastened in rotational coordinates, by i_pdcAlso throw To xy coordinate systems, its coordinate value is respectively shadow：

By i_pdcComponent on xy coordinate systems is added separately to load component of the watt current on xy axial coordinates, then be Unite consumption watt current be in the coordinate value of xy coordinate systems：

7) watt current is entered into row matrix in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage The three-phase instantaneous value that inverse transformation obtains watt current is respectively：

In formula (12),γ is first for xy coordinate systems Phase angle；

8) the three-phase instantaneous value of the system watt current for 7) obtaining is subtracted with the load current three-phase instantaneous value for collecting, i.e., The instruction current signal of Active Power Filter-APF is obtained,

When PCC electric voltage frequencies are displaced to ω ' by ω, the instruction current signal of Active Power Filter-APF is obtained in step 3 Specifically implement according to following steps：

1) instantaneous value of system PCC point voltages and load current is respectively：

In formula (14), (15), m, n are overtone order ,+positive sequence is represented ,-represent negative phase-sequence；ω₀It is angular speed, when t is Between,It is positive sequence m subharmonic voltage amplitudes,It is negative phase-sequence m subharmonic voltage amplitudes,At the beginning of negative phase-sequence m subharmonic voltages Beginning phase angle,It is the initial phase angle of positive sequence m subharmonic voltages,It is positive sequence nth harmonic current amplitude,For negative phase-sequence n times is humorous Ripple current amplitude,It is the initial phase angle of negative phase-sequence nth harmonic electric current,It is the initial phase angle of positive sequence nth harmonic electric current；

2) voltage and load current instantaneous value of PCC points are converted into two-phase rest frame；

Coordinate value of the voltage of PCC points in two-phase rest frame be：

In formula (16), (17),

3) voltage vector, electric current arrow are converted to according to the locus between two-phase rest frame and rotating coordinate system The coordinate value that amount is fastened in rotational coordinates；

Voltage vector is in the coordinate value that rotational coordinates is fastened：

In formula (18),γ is the first angle of xy coordinate systems；

Current phasor is in the coordinate value that rotational coordinates is fastened：

4) coordinate value that voltage vector is fastened in rotational coordinates is extracted using low pass filter, obtains PCC point voltages and bear Carry current first harmonics positive-sequence component is in the coordinate value that rotational coordinates is fastened：

In formula (20),It is fundamental positive sequence voltage, the amplitude of electric current,It is fundamental positive sequence voltage, electricity The initial phase angle of stream, γ is the initial phase angle of xy coordinate systems；

5) according to 3) and 4) voltage, the fundamental positive sequence of electric current obtained in fundamental positive sequence voltage same rotating speed in the same direction The coordinate value fastened of rotational coordinates, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is

Further according to the definition of watt current, to obtain watt current expression formula as follows：

In formula (21),

Then watt current is in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage：

6) according to DC voltage and the deviation of desired value, the watt current needed for obtaining voltage control using PI controllers i_pdc, further according to the coordinate value that the PCC point voltage fundamental positive-sequence components obtained in step 3.4 are fastened in rotational coordinates, by i_pdc Xy coordinate systems are projected to, its coordinate value is respectively：

By i_pdcComponent on xy coordinate systems is added separately to load component of the watt current on xy axial coordinates, then be Unite consumption watt current be in the coordinate value of xy coordinate systems：

7) watt current is entered into row matrix in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage The three-phase instantaneous value that inverse transformation obtains watt current is respectively：

In formula (25),γ is first for xy coordinate systems Phase angle；

8) the three-phase instantaneous value of the system watt current obtained in being subtracted 7) with the load current three-phase instantaneous value for collecting, The instruction current signal of Active Power Filter-APF is obtained final product,

Step 4, dsp processor is by instruction current signal i_refa、i_refb、i_refcWith data signal i_ca、i_cbAnd i_ccCarry out stagnant Ring compares, and controls the PWM module of DSP to send PWM ripples；

Step 5, the PWM ripples that dsp processor is sent are sent to the drive circuit of the IGBT module of inverter, control inversion Device is according to instruction current signal i_refa、i_refb、i_refcSend electric current, according to the harmonic wave that sends in the weak network system of current compensation and Reactive power.

Active Power Filter-APF Direct Current Control method of the present invention under weak grid conditions, active electric power filter Ripple device, i.e. APF, using the voltage source inverter of phase three-wire three, the structure being connected with light current net is as shown in figure 1, e_a、e_b、e_cFor Voltage at PCC points, i_sa、i_sb、i_scIt is the electric current that PCC points absorb from power network, i_La、i_Lb、i_LcFor the electricity that nonlinear load absorbs Stream, i_ca、i_cb、i_ccIt is the electric current that inverter sends, R, L, C are respectively connection impedance and the DC bus capacitor of inverter.Z_ga、 Z_gb、Z_gcIt is electric network impedance.

The present invention is applied to the Active Power Filter-APF Direct Current Control method under weak grid conditions, according to voltage and electricity The vectorial property of stream is deduced a kind of rotating vector detection method based on virtual synchronous coordinate system, and coordinate transform is as shown in Figure 2. The dq coordinate systems in conventional method are instead of using the xy coordinate systems with the PCC point synchronized rotating Vortexes of fundamental positive sequence voltage, due to The initial phase angle of xy coordinate systems can be arbitrary value, therefore not need the PLL to carry out phase-angle detection, corresponding to the Coordinate Conversion of Fig. 2 Matrix is：

In formula (27), γ is the angle of positive sequence fundamental voltage and x-axis.

The voltage and load current of PCC points are transformed on virtual synchronous coordinate system xy, its corresponding coordinate value is：

The coordinate value of positive sequence fundamental voltage and current phasor on xy coordinate systems is obtained by low pass filter：

Therefore the active component of positive sequence fundamental current is under xy coordinate systems：

Inverse transformation is carried out to testing result, the active component for obtaining positive sequence fundamental current is：

The value for caning be found that virtual rotating coordinate system angle by above-mentioned testing result does not interfere with testing result.

The DC capacitor voltage fluctuation of APF can not only influence its compensation effect, and can influence the stabilization of whole system Property.In the dynamic processes such as APF startups, grid-connected and load switching, the control to its DC voltage is necessary.Tradition control According to DC voltage and the deviation of desired value in system strategy, the watt current needed for obtaining voltage control using PI controllers i_pdc, and add it to realize in load current d axle components the closed-loop control of DC voltage.

Although xy coordinate systems and the synchronized rotating Vortex of dq coordinate systems, there is angle γ in it and positive sequence fundamental voltage between, It is of the invention by i and γ values are time-varying_pdcAlso xy coordinate systems are projected to, its coordinate value is respectively：

By i_pdcComponent on xy coordinate systems is added separately to load component of the watt current on xy axial coordinates, realizes With DC voltage closed-loop control equivalent in Traditional control.

As shown in figure 3, under the conditions of the PCC voltage distortions and imbalance of weak network system, APF no longer needs to apply PLL (i.e. phaselocked loop) detection voltage phase, therefore the complexity of control algolithm is reduced, while reducing by PLL introduced detection Time delay, is effectively improved the performance of APF.

When the light current net system operation containing a large amount of distributed power sources is in the case of isolated island when, because unbalanced power can draw Line voltage frequency deviation is played, the present disclosure applies equally to this kind of situation.Assuming that power network fundamental voltage frequency is displaced to ω ' by ω, it is right The electric current answered can equally occur frequency deviation, transform to after virtual synchronous coordinate system by low pass filter obtain positive sequence fundamental voltage and Coordinate value of the current phasor on xy coordinate systems be：

The active component of positive sequence fundamental current is under xy coordinate systems：

Therefore the active component of three-phase positive sequence fundamental current is：

By formula (36) as can be seen that when PCC points voltage occurs frequency deviation, the present invention can accurately carry out current detecting.

System shown in Figure 1 is emulated in Matlab/Simulink softwares, PCC point voltages are folded by positive sequence fundamental voltage Plus negative phase-sequence 5 times and the subharmonic voltage of positive sequence 7 are constituted, and are loaded as three-phase bridge can not control rectifying circuit, specific system emulation parameter As shown in table 1：

The system emulation parameter of table 1

Using Matlab/Simulink softwares, the system emulation parameter in table 1 obtains the emulation shown in Fig. 4-16 Result figure；

Fig. 4, Fig. 5 are respectively PCC point voltages and load current waveform before APF inputs.Wherein negative phase-sequence 5 subharmonic voltage Perunit value is 0.3, and the perunit value of the subharmonic voltage of positive sequence 7 is 0.15.

Fig. 6, Fig. 7, Fig. 8, Fig. 9 are respectively APF control methods and compensate forward and backward PCC point A phase voltages and power network inflow PCC points The waveform of electric current and the fft analysis result of electric current.Before APF puts into operation, the total harmonic distortion factor of inflow current is There is certain phase angle difference between 25.66%, and voltage and current, system power factor is 0.886；APF put into operation with Afterwards, the current total harmonic distortion rate of power network inflow PCC points is reduced to 1.71%, and electric current and positive sequence fundamental voltage same-phase, System power factor brings up to 1.0, and, when weak network system is in stable state, APF can effectively accurate compensation load for the present invention Idle harmonic electric current.

Weak network system is put in the load of 0.5s non-linear hours and is twice, and Figure 10, Figure 11, Figure 12 sets forth load current Waveform, the electric current that the A phase currents and its reference value waveform of APF outputs and weak network system PCC point A phase voltages and power network are flowed into Waveform.Show APF using the present invention, dynamic tracing compensation can be completed within an electric cycle, dynamic response characteristic is good.

Figure 13, Figure 14 sets forth light current net system voltage in 0.5s under generation ± 5Hz offset frequency situations, and PCC points are electric Pressure and power network flow into the waveform of PCC point electric currents, and Figure 15, Figure 16 sets forth the fft analysis of electric current, from the and of Figure 13,14,15 Can find out that the power network inflow current after compensation can keep by the adjustment of a cycle when system voltage occurs frequency deviation in 16 With voltage in phase, and total harmonic distortion factor is respectively 2.45%, 2.04%.Therefore by weak line voltage there is no frequency in the present invention Inclined influence.

Claims (1)

1. the Active Power Filter-APF Direct Current Control method under weak grid conditions is applied to, it is characterised in that according to following Step is implemented：

Step 1, gathers voltage e at weak network system PCC points_a、e_bAnd e_cInstantaneous value, DC side voltage of converter v_dcIt is instantaneous Value, load current i_La、i_LbAnd i_LcInstantaneous value, and the electric current i that inverter sends_ca、i_cbAnd i_ccInstantaneous value；

Step 2, the e that will be collected_a、e_b、e_c、v_dc、i_La、i_LbAnd i_LcInstantaneous value, and the electric current i that inverter sends_ca、i_cb And i_ccInstantaneous value is converted to data signal e in being input to dsp processor after modulate circuit treatment by A/D modules_a、e_b、 e_c、v_dc、i_La、i_Lb、i_Lc、i_ca、i_cbAnd i_cc；

Step 3, dsp processor is by data signal e_a、e_b、e_c、v_dc、i_La、i_LbAnd i_LcProcessed, obtained active electric power filter The instruction current signal i of ripple device_refa、i_refb、i_refc；

The instruction current signal that Active Power Filter-APF is obtained in step 3 is specifically implemented according to following steps：

1) instantaneous value for setting system PCC point voltages and load current is respectively：

$\left\{\begin{array}{c}{e}_a=\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[E_m^{+}\sin (m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{+})+E_m^{-}\sin (m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{-})\]\\ e_b=\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[E_m^{+}\sin (m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{+}-2\mathrm{\π}/3)+E_m^{-}\sin (m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{-}+2\mathrm{\π}/3)\]\\ e_c=\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[E_m^{+}\sin (m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{+}+2\mathrm{\π}/3)+E_m^{-}\sin (m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{-}-2\mathrm{\π}/3)\]\end{array}\right.---\left(1\right)$

In formula (1), (2)：M, n are overtone order ,+positive sequence is represented ,-represent negative phase-sequence；ω is angular speed, and t is the time,For just Sequence m subharmonic voltage amplitudes,It is negative phase-sequence m subharmonic voltage amplitudes,It is the initial phase angle of negative phase-sequence m subharmonic voltages,For The initial phase angle of positive sequence m subharmonic voltages,It is positive sequence nth harmonic current amplitude,It is negative phase-sequence nth harmonic current amplitude, It is the initial phase angle of negative phase-sequence nth harmonic electric current,It is the initial phase angle of positive sequence nth harmonic electric current；

2) voltage and load current instantaneous value of PCC points are converted into two-phase rest frame；

Coordinate value of the voltage of PCC points in two-phase rest frame be：

$\left[\begin{array}{c}{e}_{\mathrm{\α}}\\ e_{\mathrm{\β}}\end{array}\right]=C_{abc\_\mathrm{\α}\mathrm{\β}}\left[\begin{array}{c}{e}_a\\ e_b\\ e_c\end{array}\right]=\left[\begin{array}{c}\sqrt{3/2}\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[E_m^{+}\sin (m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{+})+E_m^{-}\sin (m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{-})\]\\ \sqrt{3/2}\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[-E_m^{+}cos(m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{+})+E_m^{-}\cos (m\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{-})\]\end{array}\right]---\left(3\right)$

In formula (3), (4)：

3) voltage vector, current phasor is converted to according to the locus between two-phase rest frame and rotating coordinate system to exist The coordinate value that rotational coordinates is fastened；

Voltage vector is in the coordinate value that rotational coordinates is fastened：

$\begin{array}{c}\left[\begin{array}{c}{e}_x\\ e_y\end{array}\right]=C_{\mathrm{\α}\mathrm{\β}\_xy}\left[\begin{array}{c}{e}_{\mathrm{\α}}\\ e_{\mathrm{\β}}\end{array}\right]\\ =\left[\begin{array}{c}\sqrt{3/2}\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\{E_m^{+}\cos \[(m-1)\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{+}-\mathrm{\γ}\]-E_m^{-}\cos \[(m+1)\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{-}+\mathrm{\γ}\]\}\\ -\sqrt{3/2}\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\{E_m^{+}\sin \[(m-1)\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{+}-\mathrm{\γ}\]+E_m^{-}\sin \[(m+1)\mathrm{\ω}t+{\mathrm{\θ}}_{em}^{-}+\mathrm{\γ}\]\}\end{array}\right]\end{array}---\left(5\right)$

In formula (5),γ is the initial phase angle of xy coordinate systems；

Current phasor is in the coordinate value that rotational coordinates is fastened：

4) coordinate value that voltage vector is fastened in rotational coordinates is extracted using low pass filter, obtains PCC point voltages and load electricity Flow fundamental positive sequence is in the coordinate value that rotational coordinates is fastened：

In formula (7),It is fundamental positive sequence voltage, the amplitude of electric current,For fundamental positive sequence voltage, electric current just Beginning phase angle, γ is the initial phase angle of xy coordinate systems；

5) according to 3) and 4) voltage, the fundamental positive sequence of electric current obtained in fundamental positive sequence voltage in the same direction with the rotation of rotating speed Turn the coordinate value on coordinate system, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is

Definition further according to watt current obtains watt current, and expression is as follows：

In formula (8),

Then watt current is in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage：

$\left\{\begin{array}{c}{i}_{\mathrm{pLx}}=i_p\cos ({\mathrm{\θ}}_1^{+}-\mathrm{\γ})=\frac{(e_{x1}^{+}{i}_{x1}^{+}+e_{y1}^{+}{i}_{y1}^{+})e_{x1}^{+}}{{\left(e_{x1}^{+}\right)}^2+{\left(e_{y1}^{+}\right)}^2}\\ i_{\mathrm{pLy}}=i_p\sin ({\mathrm{\θ}}_1^{+}-\mathrm{\γ})=-\frac{(e_{x1}^{+}{i}_{x1}^{+}+e_{y1}^{+}{i}_{y1}^{+})e_{y1}^{+}}{{\left(e_{x1}^{+}\right)}^2+{\left(e_{y1}^{+}\right)}^2}\end{array}\right.---\left(9\right)$

6) according to DC voltage and the deviation of desired value, the watt current i needed for obtaining voltage control using PI controllers_pdc, 3) and 4) further according to the coordinate value that the PCC point voltage fundamental positive-sequence components obtained in are fastened in rotational coordinates, by i_pdcAlso project to Xy coordinate systems, its coordinate value is respectively：

$\left\{\begin{array}{c}{i}_{\mathrm{pdcx}}=i_{\mathrm{pdc}}\×\frac{e_x}{\sqrt{e_x^2+e_y^2}}\\ i_{\mathrm{pdcy}}=i_{\mathrm{pdc}}\×\frac{e_y}{\sqrt{e_x^2+e_y^2}}\end{array}\right.---\left(10\right)$

By i_pdcComponent on xy coordinate systems is added separately to load component of the watt current on xy axial coordinates, then system disappears The watt current of consumption is in the coordinate value of xy coordinate systems：

$\left\{\begin{array}{c}{i}_{px}=i_{pLx}+i_{pdcx}\\ i_{py}=i_{pLy}+i_{pdcy}\end{array}\right.---\left(11\right)$

7) watt current is entered into row matrix contravariant in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage The three-phase instantaneous value for getting watt current in return is respectively：

In formula (12),γ is the initial phase angle of xy coordinate systems；

8) the three-phase instantaneous value of the system watt current for 7) obtaining is subtracted with the load current three-phase instantaneous value for collecting, has been obtained final product The instruction current signal of active power filter,

$\left\{\begin{array}{c}{i}_{refa}=i_{La}-i_{pa}\\ i_{refb}=i_{Lb}-i_{pb}\\ i_{refc}=i_{Lc}-i_{pc}\end{array}\right.---\left(13\right)$

When PCC electric voltage frequencies are displaced to ω ' by ω, the instruction current signal that Active Power Filter-APF is obtained in step 3 is specific Implement according to following steps：

1) instantaneous value for setting system PCC point voltages and load current is respectively：

$\left\{\begin{array}{c}{e}_a=\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[E_m^{+}\sin ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{+})+E_m^{-}\sin ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{-})\]\\ e_b=\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[E_m^{+}\sin ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{+}-2\mathrm{\π}/3)+E_m^{-}\sin ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{-}+2\mathrm{\π}/3)\]\\ e_c=\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[E_m^{+}\sin ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{+}+2\mathrm{\π}/3)+E_m^{-}\sin ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{-}-2\mathrm{\π}/3)\]\end{array}\right.---\left(14\right)$

In formula (14), (15), m, n are overtone order ,+positive sequence is represented ,-represent negative phase-sequence；ω₀It is angular speed, t is the time, It is positive sequence m subharmonic voltage amplitudes,It is negative phase-sequence m subharmonic voltage amplitudes,It is the initial phase angle of negative phase-sequence m subharmonic voltages,It is the initial phase angle of positive sequence m subharmonic voltages,It is positive sequence nth harmonic current amplitude,It is negative phase-sequence nth harmonic electric current width Value,It is the initial phase angle of negative phase-sequence nth harmonic electric current,It is the initial phase angle of positive sequence nth harmonic electric current；

2) voltage and load current instantaneous value of PCC points are converted into two-phase rest frame；

Coordinate value of the voltage of PCC points in two-phase rest frame be：

$\left[\begin{array}{c}{e}_{\mathrm{\α}}\\ e_{\mathrm{\β}}\end{array}\right]=C_{abc\_\mathrm{\α}\mathrm{\β}}\left[\begin{array}{c}{e}_a\\ e_b\\ e_c\end{array}\right]=\left[\begin{array}{c}\sqrt{3/2}\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[E_m^{+}\sin ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{+})+E_m^{-}\sin ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{-})\]\\ \sqrt{3/2}\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\[-E_m^{+}\cos ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{+})+E_m^{-}\cos ({\mathrm{m\ω}}^{\′}t+{\mathrm{\θ}}_{em}^{-})\]\end{array}\right]---\left(16\right)$

In formula (16), (17),

3) voltage vector, current phasor is converted to according to the locus between two-phase rest frame and rotating coordinate system to exist The coordinate value that rotational coordinates is fastened；

Voltage vector is in the coordinate value that rotational coordinates is fastened：

$\begin{array}{c}\left[\begin{array}{c}{e}_x\\ e_y\end{array}\right]=C_{\mathrm{\α}\mathrm{\β}\_xy}\left[\begin{array}{c}{e}_{\mathrm{\α}}\\ e_{\mathrm{\β}}\end{array}\right]\\ =\left[\begin{array}{c}\sqrt{3/2}\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\{E_m^{+}\cos \[({\mathrm{m\ω}}^{\′}-\mathrm{\ω})t+{\mathrm{\θ}}_{em}^{+}-\mathrm{\γ}\]-E_m^{-}\cos \[({\mathrm{m\ω}}^{\′}+\mathrm{\ω})t+{\mathrm{\θ}}_{em}^{-}+\mathrm{\γ}\]\}\\ -\sqrt{3/2}\underset{m=1}{\overset{\mathrm{\∞}}{\mathrm{\Σ}}}\{E_m^{+}\sin \[({\mathrm{m\ω}}^{\′}-\mathrm{\ω})t+{\mathrm{\θ}}_{em}^{+}-\mathrm{\γ}\]+E_m^{-}\sin \[({\mathrm{m\ω}}^{\′}+\mathrm{\ω})t+{\mathrm{\θ}}_{em}^{-}+\mathrm{\γ}\]\}\end{array}\right]\end{array}---\left(18\right)$

In formula (18),γ is the first angle of xy coordinate systems；

Current phasor is in the coordinate value that rotational coordinates is fastened：

4) coordinate value that voltage vector is fastened in rotational coordinates is extracted using low pass filter, obtains PCC point voltages and load electricity Flow fundamental positive sequence is in the coordinate value that rotational coordinates is fastened：

In formula (20),It is fundamental positive sequence voltage, the amplitude of electric current,It is fundamental positive sequence voltage, electric current Initial phase angle, γ is the initial phase angle of xy coordinate systems；

5) according to 3) and 4) voltage, the fundamental positive sequence of electric current obtained in fundamental positive sequence voltage in the same direction with the rotation of rotating speed Turn the coordinate value on coordinate system, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is

Further according to the definition of watt current, to obtain watt current expression formula as follows：

In formula (21),

Then watt current is in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage：

6) according to DC voltage and the deviation of desired value, the watt current i needed for obtaining voltage control using PI controllers_pdc, Further according to the coordinate value that the PCC point voltage fundamental positive-sequence components obtained in step 3.4 are fastened in rotational coordinates, by i_pdcAlso project To xy coordinate systems, its coordinate value is respectively：

$\left\{\begin{array}{c}{i}_{pdcx}=i_{pdc}\×\frac{e_x}{\sqrt{e_x^2+e_y^2}}\\ i_{pdcy}=i_{pdc}\×\frac{e_y}{\sqrt{e_x^2+e_y^2}}\end{array}\right.---\left(23\right)$

By i_pdcComponent on xy coordinate systems is added separately to load component of the watt current on xy axial coordinates, then system disappears The watt current of consumption is in the coordinate value of xy coordinate systems：

$\left\{\begin{array}{c}{i}_{px}=i_{pLx}+i_{pdcx}\\ i_{py}=i_{pLy}+i_{pdcy}\end{array}\right.---\left(24\right)$

7) watt current is entered into row matrix contravariant in the coordinate value fastened with the rotational coordinates of rotating speed in the same direction with fundamental positive sequence voltage The three-phase instantaneous value for getting watt current in return is respectively：

In formula (25),γ is the initial phase angle of xy coordinate systems；

8) the three-phase instantaneous value of the system watt current obtained in being subtracted 7) with the load current three-phase instantaneous value for collecting, obtains final product The instruction current signal of Active Power Filter-APF,

$\left\{\begin{array}{c}{i}_{refa}=i_{La}-i_{pa}\\ i_{refb}=i_{Lb}-i_{pb}\\ i_{refc}=i_{Lc}-i_{pc}\end{array}\right.---\left(26\right)$

Step 4, dsp processor is by instruction current signal i_refa、i_refb、i_refcWith data signal i_ca、i_cbAnd i_ccCarry out stagnant ring ratio Compared with, and control the PWM module of DSP to send PWM ripples；

Step 5, the PWM ripples that dsp processor is sent are sent to the drive circuit of the IGBT module of inverter, and control inverter is pressed According to instruction current signal i_refa、i_refb、i_refcElectric current is sent, according to the harmonic wave sent in the weak network system of current compensation and idle Power.