CN104242618A - Signal processing method for reducing current distortion of photovoltaic inverters - Google Patents

Abstract

The invention discloses a signal processing method for reducing current distortion of photovoltaic inverters. The signal processing method is characterized by comprising steps of (1), converting voltage signals of power grids by voltage sensors, and then converting the analog signals into digital signals by A/D (analog/digital) sampling modules; (2), transmitting the digital signals to IIR (infinite impulse response) digital filter modules, digitally filtering the digital signals and then outputting sine wave signals; (3), transmitting the sine wave signals to digital shaping modules and outputting square wave signals after the sine wave signals are converted; (4), inputting the square wave signals into phase angle computing modules and computing phase angles of the voltages of the power grids; (5), converting the phase angles outputted by the phase angle computing modules and outputting PWM (pulse width modulation) control signals. The signal processing method for reducing the current distortion of the photovoltaic inverters has the advantages that the problem of high harmonic contents in grid-connected currents of existing photovoltaic inverters due to severe grid-side voltage distortion can be solved by the aid of the signal processing method, and the signal processing method is favorable for improving the quality of grid-connected currents of the grid-connected inverters.

Description

A kind of reduction photovoltaic DC-to-AC converter current distortion signal processing method

Technical field

The invention belongs to power electronics control technology field, refer more particularly to a kind of reduction photovoltaic DC-to-AC converter current distortion signal processing method.

Background technology

Parallel network power generation technology has become an important directions of utilization of new energy resources, and combining inverter is the core component of photovoltaic system, and therefore high-quality inverter becomes the emphasis of research.

In photovoltaic parallel in system, accurately and detect that the frequency of line voltage, phase place and amplitude are absolutely necessary link rapidly.When line voltage Severe distortion, easily there is the aberration problems such as zero crossing, crest, trough in inverter output current, affects the electrical network quality of power supply.And solving this problem, tradition adopts the zero crossing of digital phase-locked loop detection of grid voltage thus realizes phase-locked method, but the method poor anti jamming capability, cannot meet preferably and use needs.

Summary of the invention

The problem that the grid-connected current harmonic content seriously caused because voltage on line side distorts in order to the grid-connected current solving photovoltaic DC-to-AC converter in prior art is large, the invention provides a kind of reduction photovoltaic DC-to-AC converter current distortion signal processing method being conducive to provide the grid-connected current quality of combining inverter.

In order to solve the problem, the technical solution used in the present invention is:

A kind of reduction photovoltaic DC-to-AC converter current distortion signal processing method, is characterized in that: comprise the following steps:

(1), analog signal is converted to digital signal through A/D sampling module by mains voltage signal after voltage sensor conversion;

(2), digital data transmission to IIR digital filtering module, sine wave output signal after digital filtering;

(3), sine wave signal exports square-wave signal after flowing to the conversion of digital Shaping Module;

(4), by the computing module of square-wave signal input phase angle, the phase angle of line voltage is calculated;

(5) phase angle that, phase calculation module exports exports pwm control signal through conversion.

Aforesaid one reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: IIR digital filtering module has following constraints before filtering: 1), iir digital filter is designed to IIR digital band-pass filter, and bandwidth is no more than 100Hz; 2), the centre frequency of IIR digital band-pass filter is power frequency 50Hz or 60Hz; 3), IIR digital band-pass filter ensures to be greater than-10dB to the amplitude attenuation degree of three times and above harmonic wave.

Aforesaid one reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: in step (3), sinusoidal signal after digital filtering is square-wave signal by numeral Shaping Module, the half period that sinusoidal magnitude is greater than zero is high level, and the minus half period of amplitude is low level.

Aforesaid one reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: in step (4), arrange counter in phase calculation module,

Between the high period of square-wave signal, the phase angle theta of line voltage _gridcomputing formula is:

${\mathrm{\θ}}_{\mathrm{grid}}=360\·\frac{{\mathrm{Nf}}_{\mathrm{grid}}}{f_s},$

Between the low period of square-wave signal, the phase angle theta of line voltage _gridcomputing formula is:

${\mathrm{\θ}}_{\mathrm{grid}}=360\·\frac{{\mathrm{Nf}}_{\mathrm{grid}}}{f_s}+180,$

Wherein, N is Counter Value, f _gridfor line voltage frequency, f _sfor switching frequency.

Aforesaid one reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: in step (5), the phase angle that the grid-connected current reference signal of the PWM control module of inverter is exported by phase calculation module calculates or lookup table mode acquisition through SIN function

Grid-connected current reference signal i _reffor:

i _ref＝sin(θ _grid)

The grid-connected current reference signal i obtained _refthe overlapping output pwm control signal with triangular wave again.

Aforesaid one reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: in step (4), at rising edge and the trailing edge position clearing counting of square-wave signal, prevents counting error from accumulating.

Aforesaid one reduces photovoltaic DC-to-AC converter current distortion signal processing method, and it is characterized in that: because the convergence process of IIR digital filtering algorithm is longer, the output of pwm control signal need arrange regular hour time delay, to prevent the control logic of mistake from exporting,

The setting of delay time can refer to following formula and carries out:

$T_{\mathrm{delay}}=n\frac{N_{\mathrm{IIR}}}{d_{\mathrm{dsp}}}$

In formula, N _iIRfor the total number of instructions of IIR algorithm, f _dspfor the dominant frequency of computation processor, n is IIR algorithm iteration calculation times, gets 100 ~ 200, adjusts according to experimental test.

The beneficial effect that the present invention reaches: digital filter of the present invention has that structure is simple, coefficient is few, multiply operation is few, efficiency is high, can resolve control, the advantage that the zero phase in characteristic frequency being convenient to realize signal offsets.Utilize iir digital filter can solve grid-connected current aberration problems because actual electric network voltage distortion causes, be conducive to the grid-connected current quality improving combining inverter, the method can be applicable in single-phase, three-phase grid-connected inverter.

Accompanying drawing explanation

Fig. 1 is that the present invention reduces photovoltaic DC-to-AC converter current distortion signal processing method structural representation.

Embodiment

Below in conjunction with accompanying drawing, the invention will be further described.Following examples only for technical scheme of the present invention is clearly described, and can not limit the scope of the invention with this.

As shown in Figure 1, a kind of reduction photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: comprise the following steps: by mains voltage signal after voltage sensor is changed successively through A/D sampling module, IIR digital filtering module, digital Shaping Module and phase angle computing module, finally obtain actual grid phase angle information.

IIR digital filtering module has following constraints before filtering: 1), iir digital filter is designed to IIR digital band-pass filter, and bandwidth is no more than 100Hz; 2), the centre frequency of IIR digital band-pass filter is power frequency 50Hz or 60Hz; 3), IIR digital band-pass filter ensures to be greater than-10dB to the amplitude attenuation degree of three times and above harmonic wave.

Matlab DSPToolBox Filter Design and Analysis Tool (FDA Tool) of MATLAB is utilized to carry out design and analysis filter.Successively to the fundamental type (high pass, low pass, band lead to, be with resistance) of filter, filter design method (least square method, window function metht, Butterworth method, Chebyshev I method, Chebyshev II method and elliptic filter method), filter order, sample frequency, the parameters such as cut-off frequecy of passband (upper limit, lower limit) and frequency of fadings are arranged, the last parameters automatically generating iir filter, also can generate amplitude-frequency and the phase-frequency characteristic curve of filter simultaneously.

The present invention reduces photovoltaic DC-to-AC converter current distortion signal processing method, and concrete steps are:

(1), analog signal is converted to digital signal through A/D sampling module by mains voltage signal after voltage sensor conversion.

(2), digital data transmission to IIR digital filtering module, sine wave output signal after digital filtering.

(3), the sinusoidal signal after digital filtering is square-wave signal by digital Shaping Module, and the half period that sinusoidal magnitude is greater than zero is high level, and the minus half period of amplitude is low level.

(4), counter is set in phase calculation module, calculates the phase angle of actual electric network according to the fixed switching frequency of inverter,

Between the high period of square-wave signal, the phase angle theta of line voltage _gridcomputing formula is:

${\mathrm{\θ}}_{\mathrm{grid}}=360\·\frac{{\mathrm{Nf}}_{\mathrm{grid}}}{f_s},$

Between the low period of square-wave signal, the phase angle theta of line voltage _gridcomputing formula is:

${\mathrm{\θ}}_{\mathrm{grid}}=360\·\frac{{\mathrm{Nf}}_{\mathrm{grid}}}{f_s}+180,$

Wherein, N is Counter Value, f _gridfor line voltage frequency, f _sfor switching frequency.

(5) phase angle that, the grid-connected current reference signal of the PWM control module of inverter is exported by phase calculation module calculates through SIN function or lookup table mode obtains, reset counter in the rising and falling edges position of square-wave signal, prevent counting error from accumulating.

Grid-connected current reference signal i _reffor:

i _ref＝sin(θ _grid)

The grid-connected current reference signal i obtained _refthe overlapping output pwm control signal with triangular wave again.

(6), because the convergence process of IIR digital filtering algorithm is longer, the output of pwm control signal need arrange regular hour time delay, exports to prevent the control logic of mistake.

The setting of delay time can refer to following formula and carries out:

$T_{\mathrm{delay}}=n\frac{N_{\mathrm{IIR}}}{f_{\mathrm{dsp}}}$

In formula, N _iIRfor the total number of instructions of IIR algorithm, f _dspfor the dominant frequency of computation processor, n is IIR algorithm iteration calculation times, gets 100 ~ 200, adjusts according to experimental test.

The present invention, on the basis not increasing inverter hardware cost, improves the problem that harmonic current that combining inverter output current brings because line voltage distorts is large, has that cost is low, the feature of highly versatile.The power quality problem brought for solving distributed photovoltaic power generation extensive development provides a kind of new resolving ideas.

More than show and describe general principle of the present invention, principal character and advantage.The technical staff of the industry should understand; the present invention is not restricted to the described embodiments; what describe in above-described embodiment and specification just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and these changes and improvements all fall in the claimed scope of the invention.Application claims protection range is defined by appending claims and equivalent thereof.

Claims (7)

1. reduce a photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: comprise the following steps:

(1), analog signal is converted to digital signal through A/D sampling module by mains voltage signal after voltage sensor conversion;

(2), digital data transmission to IIR digital filtering module, sine wave output signal after digital filtering;

(3), sine wave signal exports square-wave signal after flowing to the conversion of digital Shaping Module;

(4), by the computing module of square-wave signal input phase angle, the phase angle of line voltage is calculated;

(5) phase angle that, phase calculation module exports exports pwm control signal through conversion.

2. one according to claim 1 reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: IIR digital filtering module has following constraints before filtering: 1), iir digital filter is designed to IIR digital band-pass filter, and bandwidth is no more than 100Hz; 2), the centre frequency of IIR digital band-pass filter is power frequency 50Hz or 60Hz; 3), IIR digital band-pass filter ensures to be greater than-10dB to the amplitude attenuation degree of three times and above harmonic wave.

3. one according to claim 2 reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: in step (3), sinusoidal signal after digital filtering is square-wave signal by numeral Shaping Module, the half period that sinusoidal magnitude is greater than zero is high level, and the minus half period of amplitude is low level.

4. one according to claim 3 reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: in step (4), arrange counter in phase calculation module,

Between the high period of square-wave signal, the phase angle theta of line voltage _gridcomputing formula is:

${\mathrm{\θ}}_{\mathrm{grid}}=360\·\frac{{\mathrm{Nf}}_{\mathrm{grid}}}{f_s},$

Between the low period of square-wave signal, the phase angle theta of line voltage _gridcomputing formula is:

${\mathrm{\θ}}_{\mathrm{grid}}=360\·\frac{{\mathrm{Nf}}_{\mathrm{grid}}}{f_s}+180,$

Wherein, N is Counter Value, f _gridfor line voltage frequency, f _sfor switching frequency.

5. one according to claim 4 reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: in step (5), the phase angle that the grid-connected current reference signal of the PWM control module of inverter is exported by phase calculation module calculates or lookup table mode acquisition through SIN function

Grid-connected current reference signal i _reffor:

i _ref＝sin(θ _grid)

The grid-connected current reference signal i obtained _refthe overlapping output pwm control signal with triangular wave again.

6. one according to claim 5 reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: in step (4), at rising edge and the trailing edge position clearing counting of square-wave signal, prevents counting error from accumulating.

7. one according to claim 6 reduces photovoltaic DC-to-AC converter current distortion signal processing method, it is characterized in that: because the convergence process of IIR digital filtering algorithm is longer, the output of pwm control signal need arrange regular hour time delay, exports to prevent the control logic of mistake

The setting of delay time can refer to following formula and carries out:

$T_{\mathrm{delay}}=n\frac{N_{\mathrm{IIR}}}{f_{\mathrm{dsp}}}$

In formula, N _iIRfor the total number of instructions of IIR algorithm, f _dspfor the dominant frequency of computation processor, n is IIR algorithm iteration calculation times, gets 100 ~ 200.