CN103094918B - A kind of single-phase grid-connected device improving the quality of power supply - Google Patents

Abstract

The present invention discloses a kind of single-phase grid-connected device improving the quality of power supply, and comprise the single-phase electricity die mould inverter based on all-controlling power electronics device, the DC side of single-phase electricity die mould inverter is connected with distributed generation system; Also comprise one end and inverter and export the other end that is connected accesses electric power system grid-connected electric capacity C by filter inductance _inv, and suppress the filter inductance L of inverter output current high frequency components _filter, grid-connected electric capacity C _invreactance be greater than filter inductance L _filterreactance.The present invention can reduce the DC capacitor voltage of combining inverter, reduces cost and the switching loss of switch element, realizes the active power being injected distributed power source generation by combining inverter to system, and can improve the quality of power supply simultaneously.

Description

A kind of single-phase grid-connected device improving the quality of power supply

Technical field

The present invention relates to the distributed power generation in electric power system and power quality controlling, belong to the Semiconductor Converting Technology field in electrical engineering.

Background technology

Traditional fossil energy reduces day by day, obtains development and apply fast with the new forms of energy that wind energy, solar energy are representative.The generating equipment of new forms of energy, had both comprised jumbo centralized electricity generation system, had also comprised the distributed power generation unit of low capacity.The wind-driven generator of low capacity, photovoltaic array also usually with the energy storage devices such as battery with the use of, become a distributed generation system.By the electric energy of distributed generation system access low-voltage network for user, to need through a series of ac-dc conversion.Last link wherein converted often is completed by combining inverter direct current being converted into interchange.This combining inverter parallel connection access low voltage electric network, and control the energy exchange between electrical network and distributed generation system.

Combining inverter not only can inject to system the active power that distributed power source sends, and can also have both the function of reactive power compensation, harmonic wave control simultaneously.Traditional grid-connecting apparatus connects inverter output end and electrical network often through reactor, and in order to realize above-mentioned functions, the output voltage of inverter must meet certain requirement.As when inverter accesses 220V electrical network, inverter output voltage needs the level reached higher than line voltage, and corresponding DC side voltage of converter is just higher than the peak value of line voltage.

Because the output voltage of distributed power source is often lower, partial devices is by improving output voltage at combining inverter AC access step-up transformer, thus access electrical network, as " a kind of combining inverter and parallel network reverse control method with complex function " (Chinese invention patent, publication date: on February 15th, 2012, application publication number: CN 102355151 A).If avoid using step-up transformer, the output voltage of distributed power source is just needed to be improved by extra link, inverter just can be made to access power distribution network, the way of general employing DC/DC converter boost realizes, as " solar photovoltaic interconnected inverter " (Chinese invention patent, authorized announcement date on September 28th, 2011, Authorization Notice No. CN 101304224 B) and " have both reactive power compensation, the photovoltaic of harmonic wave control function, wind-powered electricity generation unify grid-connecting apparatus " (Chinese invention patent, publication date: on August 15th, 2007, publication number CN101017982A).But when the no-load voltage ratio of DC/DC converter is higher, structure can be more complicated, and in the conversion process of boosted voltage, efficiency also declines to some extent.

Summary of the invention

The object of the invention is the DC capacitor voltage in order to reduce combining inverter, reduce cost and the switching loss of switch element, there is provided a kind of, by grid-connected electric capacity and filter inductance, inverter is accessed distribution system, realize the active power being injected distributed power source generation by combining inverter to system, and the single-phase grid-connected device of the quality of power supply can be improved simultaneously.

In order to realize above object, the invention provides a kind of single-phase grid-connected device improving the quality of power supply, comprise the single-phase electricity die mould inverter based on all-controlling power electronics device, the DC side of single-phase electricity die mould inverter is connected with distributed generation system; Also comprise one end and inverter and export the other end that is connected accesses electric power system grid-connected electric capacity C by filter inductance _inv, and suppress the filter inductance L of inverter output current high frequency components _filter, grid-connected electric capacity C _invreactance be greater than filter inductance L _filterreactance.

In said apparatus, described filter inductance and grid-connected capacitor resonance are at a certain subfrequency of distribution system.In said apparatus, described grid-connected electric capacity C _invwith filter inductance L _filtersize obtain by the following method: first, determine grid-connected electric capacity C by following formula _invwith filter inductance L _filterthe impedance X of the series arm formed _cf:

$X_{\mathrm{Cf}}=\frac{V_S^2}{Q_0}$

Wherein, V _sthe system voltage of inverter access point, Q ₀it is design reactive power; Afterwards, grid-connected electric capacity C is calculated according to following formula group _invwith filter inductance L _filtersize:

$X_{\mathrm{Cf}}=\frac{1}{\mathrm{\ω}{C}_{\mathrm{in\; v}}}-\mathrm{\ω}{L}_{\mathrm{filter}}$

$\frac{1}{\mathrm{N\ω}{C}_{\mathrm{inv}}}-\mathrm{N\ω}{L}_{\mathrm{filter}}=0$

Wherein, ω=2 π f, f are the operating frequencies of distribution system, and N is selected filter inductance and the grid-connected capacitor resonance harmonic number in system.

Technical scheme provided by the invention, owing to have employed grid-connected electric capacity, injects active power when providing reactive power compensation and harmonic compensation, the DC voltage of inverter may operate in the level being significantly less than system voltage peak value at combining inverter to system.The reduction of DC voltage reduces the requirement of withstand voltage of selected all-controlling power electronics device, decreases the switching loss in invertor operation while reducing apparatus cost.The single-phase grid-connected device of the improvement quality of power supply proposed, not only can inject the electric energy of distributed power source as wind-driven generator, photovoltaic array generation to system, can also improve the power factor of system simultaneously, reduce system harmonics.Often output-power fluctuation is larger to consider distributed generation system, combining inverter is more difficult to be run for a long time under rated capacity, and combining inverter provides power quality controlling function, can improve utilization rate of equipment and installations, bring extra benefit, that shortens whole grid-connecting apparatus returns this cycle.

Accompanying drawing explanation

Fig. 1 is the single-phase grid-connected apparatus structure schematic diagram improving the quality of power supply provided by the invention;

Fig. 2 is the equivalent electric circuit improving the single-phase grid-connected device of the quality of power supply provided by the invention;

Fig. 3 is vectogram when improving the single-phase grid-connected plant running of the quality of power supply provided by the invention;

Fig. 4 is the vectogram of single-phase grid-connected plant running when designing reactive power improving the quality of power supply provided by the invention;

Fig. 5 is the equivalent electric circuit of the unidirectional grid-connecting apparatus adopting grid-connected inductance;

Fig. 6 is vectogram when adopting the unidirectional grid-connecting apparatus of grid-connected inductance to run;

Fig. 7 is the equivalent electric circuit of single-phase grid-connected device when compensation harmonic improving the quality of power supply provided by the invention;

Fig. 8 is the control principle block diagram of single-phase grid-connected device in emulation example improving the quality of power supply provided by the invention;

Fig. 9 provides meritorious and idle and the voltage of harmonic compensation and current waveform figure for emulating in example the single-phase grid-connected device improving the quality of power supply provided by the invention to system;

Figure 10 is direct voltage when emulating that in example, the single-phase grid-connected device improving the quality of power supply provided by the invention provides meritorious and idle and harmonic compensation to system, meritoriously export and idle output waveform figure.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the present invention is described in further detail.

As shown in Figure 1, a kind of single-phase grid-connected device improving the quality of power supply that the present embodiment provides, it comprises and exports based on the single-phase electricity die mould inverter (in figure in dotted line frame part) of all-controlling power electronics device (IGBT or MOSFET), one end and inverter the other end that is connected to access electric power system grid-connected electric capacity C by filter inductance _inv, suppress the filter inductance L of inverter output current high frequency components _filterand control device.Wherein, described control device is used for the power electronic device in control inverter, belongs to known techniques, so do not show in Fig. 1.The DC side of single-phase electricity die mould inverter is connected with distributed generation system, the reactive compensation capacity setting that described grid-connected electric capacity needs according to distribution system.

The single-phase grid-connected device that the present embodiment provides distribution system groundwork frequency (such as 50Hz) equivalent electric circuit as shown in Figure 2, as shown in Equation (1), in Fig. 2, electric capacity C is equivalent to grid-connected electric capacity C _invwith filter inductance L _filterseries arm, the impedance of this series arm is:

$X_{\mathrm{Cf}}=\frac{1}{\mathrm{\ωC}}=\frac{1}{{\mathrm{\ωC}}_{\mathrm{inv}}}-{\mathrm{\ωL}}_{\mathrm{filter}}---\left(1\right)$

Wherein, ω=2 π f, f are the operating frequencies of distribution system.Grid-connected electric capacity C in the present embodiment _invfor providing reactive power compensation, inductance L _filterfor filtering, grid-connected electric capacity C _invreactance will be greater than inductance L _filterreactance, thus whole branch road is equivalent to a pure capacitive branch.

The single-phase grid-connected device that the present embodiment provides can provide the reactive power compensation of continous-stable in power distribution network, and the capacitive reactances of series arm can be determined by following formula:

$X_{\mathrm{Cf}}=\frac{V_S^2}{Q_0}---\left(2\right)$

Wherein, V _sthe system voltage of combining inverter access point, Q ₀it is design reactive power.When voltage unit is volt (V), power unit is volt-ampere (VA).Consider load idle be constantly change, Q ₀can be calculated by following formula:

$Q_0=\frac{1}{T}\underset{0}{\overset{T}{\∫}}\mathrm{Qdt}---\left(3\right)$

Q ₀be actually an average power, time T wherein can select one day or one week or other time span, mainly selectes according to the load fluctuation situation of infield.According to capacitive reactances value, just according to following formula, corresponding capacitance size can be calculated.

$C=\frac{1}{{\mathrm{\ωx}}_{\mathrm{Cf}}}---\left(4\right)$

According to the positive direction of inverter output current in Fig. 2, when inverter injects active power to system, and when providing reactive-current compensation inductive load, its output current can be expressed as:

I _cf＝I _cfp-jI _cfq（5）

Wherein, I _cfprepresent active current, I _cfqrepresent reactive current.Inverter output voltage V _invcf can be calculated by formula (6),

V _invcf=V _S+V _Cf（6）

Wherein V _sthe system voltage of combining inverter access point, V _cfit is the voltage drop in equivalent electric circuit on electric capacity.Polar plot as shown in Figure 3, as can be seen from Figure 3 turn 90 degrees obtain because the voltage in equivalent electric circuit on electric capacity is electric current dextrorotation, for meeting required output current, the output voltage of inverter is lower than system voltage, and the voltage of required inverter direct-flow side electric capacity is also corresponding to be reduced greatly.When system needs the idle of compensation to be exactly design reactive power Q ₀time, inverter output voltage is vertical with system voltage, and inverter only needs to provide voltage for injecting active current, and vectogram is as shown in Figure 4.

Adopt in the single-phase grid-connected device of grid-connected inductance in tradition, the grid-connected electric capacity in Fig. 1 and filter inductance will replace by grid-connected inductance, its equivalent electric circuit is as shown in Figure 5.When the single-phase grid-connected device of the grid-connected inductance of this employing injects active power to system, and when providing reactive-current compensation inductive load, vectogram as shown in Figure 6, wherein V _lfthe voltage drop in equivalent electric circuit on inductance, inverter output voltage V _invLfcan be calculated by formula (7),

V _invLf＝V _S+V _Lf（7）

Can know from Fig. 5 and find out, the electric current required by inverter output voltage could must export higher than system voltage.The single-phase grid-connected device of the grid-connected electric capacity of employing that the voltage of corresponding inverter direct-flow side also can provide than the present embodiment is high.

When the single-phase grid-connected device that the present embodiment provides compensates the harmonic current of load generation, no longer applicable for the equivalent electric circuit of fundamental frequency in Fig. 2, new equivalent electric circuit as shown in Figure 7.When harmonic current flows through, the impedance of capacitor and inductor series arm is calculated by formula (8).

$X_{\mathrm{LCh}}=\frac{1}{\mathrm{h\ω}{C}_{\mathrm{inv}}}-\mathrm{h\ω}{L}_{\mathrm{filter}}---\left(8\right)$

Wherein h represents the number of times of harmonic wave, and in order to inject active power, compensating power and harmonic wave to system simultaneously, the output voltage of inverter can be calculated by formula (9).

$V_{\mathrm{invc}}=\sqrt{{\left(X_{\mathrm{Cf}}{I}_{\mathrm{cf}}\right)}^2+\underset{h-=2}{\overset{\∞}{\mathrm{\Σ}}}{X}_{\mathrm{LCh}}^2{I}_h^2}---\left(9\right)$

Wherein, I _hfor the harmonic compensation current that single-phase grid-connected device provides to system.

In the present embodiment, grid-connected electric capacity and the filter inductance L be connected in series between distribution system _filter, be used for suppressing the high order harmonic component of inverter output current, filter inductance can with a certain subfrequency of grid-connected capacitor resonance in system, such as 3 times, 5 times or 7 times.Assuming that to select harmonic number be N, under this subfrequency, the equiva lent impedance of capacitor and inductor series arm is zero, as shown in formula (10), can reduce the output voltage of inverter further.

$X_{\mathrm{LCN}}=\frac{1}{{\mathrm{N\ωC}}_{\mathrm{inv}}}-{\mathrm{N\ωL}}_{\mathrm{filter}}=0---\left(10\right)$

According to formula (1), (2) and (10) just can obtain the value of grid-connected electric capacity and filter inductance.Finally, the direct voltage of inverter can be selected according to formula (11).

$V_{\mathrm{dc}}\≥\sqrt{2}{V}_{\mathrm{invc}}---\left(11\right)$

The control principle block diagram of the single-phase grid-connected device that the present embodiment provides as shown in Figure 8, wherein adopted control method comprises: first, calculate single-phase instantaneous power according to system voltage and load current, and obtain the signal of its active power output from distributed generation system; The power signal of the active power then, by distributed generation system produced, the reactive power needing compensation, harmonic power and adjustment inverter direct-current voltage calculates the reference signal of inverter output current then; Afterwards, utilize stagnant ring pulse duration modulation method control inverter output current tracking reference signal, thus realize combining inverter and inject meritorious to system, and compensating reactive power and harmonic wave simultaneously.

Here is an emulation example of the present invention:

In this emulation example, it is in the single phase system of 220V that the single-phase grid-connected device of the improvement quality of power supply proposed is connected in parallel on a phase voltage, and its grid-connected electric capacity is 53uF, and filter inductance is 4mH, and DC capacitor voltage is 165V, and stagnant ring PWM frequency is 10kHz.

As shown in Figure 9 and Figure 10, Fig. 9 comprises three waveforms to simulation result, and wherein first is access point voltage waveform, and second is system side electric current, and the 3rd is load current, and both differences are exactly the electric current that combining inverter injects; In Figure 10, first waveform is inverter direct-current voltage waveform; Second meritorious waveform being combining inverter and injecting to system; Last is the reactive power that combining inverter injects to system.Grid-connecting apparatus parallel connection access electrical network of the present invention, original system side current waveform consistent with load current is changed, and for the moment of simulation run by 0.8 second, after grid-connecting apparatus access, in system, each Parameters variation is as shown in the table:

	Active power (W)	Reactive power (Var)	Power factor	Current harmonics (THD%)
					System side	710	0	0.994	6.61%
Load	800	793	0.707	16%

Claims (4)

1. improve a single-phase grid-connected device for the quality of power supply, comprise the single-phase electricity die mould inverter based on all-controlling power electronics device, the DC side of single-phase electricity die mould inverter is connected with distributed generation system; It is characterized in that: also comprise one end and inverter and export the other end that is connected accesses electric power system grid-connected electric capacity C by filter inductance _inv, and suppress the filter inductance L of inverter output current high frequency components _filter, grid-connected electric capacity C _invreactance be greater than filter inductance L _filterreactance; Described filter inductance and grid-connected capacitor resonance are at a certain subfrequency of distribution system.

2. the single-phase grid-connected device improving the quality of power supply according to claim 1, is characterized in that: described grid-connected electric capacity C _invwith filter inductance L _filtersize obtain by the following method: first, determine grid-connected electric capacity C by following formula _invwith filter inductance L _filterthe impedance X of the series arm formed _cf:

$X_{\mathrm{Cf}}=\frac{V_S^2}{Q_0}$

Wherein, V _sthe system voltage of inverter access point, Q ₀it is design reactive power; Afterwards, grid-connected electric capacity C is calculated according to following formula group _invwith filter inductance L _filtersize:

$X_{\mathrm{Cf}}=\frac{1}{\mathrm{\ω}{C}_{\mathrm{inv}}}-\mathrm{\ω}{L}_{\mathrm{filter}}$

$\frac{1}{\mathrm{N\ω}{C}_{\mathrm{inv}}}-\mathrm{N\ω}{L}_{\mathrm{filter}}=0$

Wherein, ω=2 π f, f are the operating frequencies of distribution system, and N is selected filter inductance and the grid-connected capacitor resonance harmonic number in system.

3. the single-phase grid-connected device improving the quality of power supply according to claim 2, is characterized in that, described Q ₀get an average power, calculated by following formula:

$Q_0=\frac{1}{T}\underset{0}{\overset{T}{\∫}}\mathrm{Qdt}$

Wherein, T is the time of certain length.

4. the single-phase grid-connected device of the improvement quality of power supply according to Claims 2 or 3, is characterized in that, the direct voltage V of inverter _dcselect according to following formula:

$V_{\mathrm{dc}}\≥\sqrt{2}{V}_{\mathrm{invc}}$

V _invcfor the output voltage of inverter, calculated by following formula:

$V_{\mathrm{invc}}=\sqrt{{\left(X_{\mathrm{Cf}}{I}_{\mathrm{cf}}\right)}^2+\underset{h=2}{\overset{\∞}{\mathrm{\Σ}}}{X}_{\mathrm{LCh}}^2{I}_h^2}$

X _lChfor electric capacity C grid-connected when harmonic current flows through _invwith filter inductance L _filterthe impedance of the series arm formed, is calculated by following formula:

$X_{\mathrm{LCh}}=\frac{1}{\mathrm{h\ω}{C}_{\mathrm{inv}}}-\mathrm{h\ω}{L}_{\mathrm{filter}}---\left(8\right)$

Wherein, h represents the number of times of harmonic wave; ω=2 π f, f are the operating frequencies of distribution system; I _cffor injecting active power when inverter to system, and the electric current that when providing reactive-current compensation inductive load, it exports; I _hfor the harmonic compensation current that single-phase grid-connected device provides to system.