CN105048926A - Method of combining maximum power tracking and U-f curve self-optimization for photovoltaic water pump system - Google Patents

Abstract

The invention discloses a method of maximum power tracking and U-f curve self-optimization for a photovoltaic water pump system. At relatively low frequency, output frequency f of a frequency converter is used to control output power Pm, at relatively high frequency, output voltage amplitude U of the frequency converter is used to control the output power Pm, and a power change corresponding to unit amplitude is relatively small, so that the output power of the frequency converter can be controlled finely till a water pump tracks maximum power output by a photovoltaic panel. By adoption of the method of combining the maximum power tracking and the U-f curve self-optimization for the photovoltaic water pump system, operation of a motor with optimal efficiency can be realized without acquisition of an optimal U-f curve of the motor in advance, and poles of a photovoltaic output voltage-power curve can be tracked, thereby improving overall operational efficiency of the photovoltaic water pump system.

Description

The method that maximal power tracing and the U-f curve of photovoltaic water pump system are combined from optimizing

Technical field

The invention belongs to the control technology field of photovoltaic water pump system, the method that the maximal power tracing being specifically related to a kind of photovoltaic water pump system and U-f curve are combined from optimizing.

Background technology

Water is the requisite resource of human survival, daily drinking-water, the irrigation of the mankind all need a large amount of water, but the freshwater resources required for us are stored in underground in a large number, i.e. so-called underground water, and a small amount of ground water, namely the water in rivers and lakes, but due to the development of human society, a large amount of cities and population are all away from rivers and lakes, also have the remote mountain area of part not have electrical network to access and lack surface water simultaneously, these occasions all need the needs meeting drinking-water and irrigate that draw water, so just need to adopt motor and water pump to draw water.

The 50Hz alternating current that traditional water extraction way normally adopts asynchronous machine band water pump directly to add the power frequency of electrical network drives, although such working method can reach the object of drawing water, but the flow velocity of its water outlet, lift etc. are all non-adjustable, are acknowledged as the water extraction way of not energy-conserving and environment-protective.So frequency converter conventional in Alternating Current Governor System, can saves energy in a large number because its output frequency is adjustable, and is widely used in pumping for water pump field.Initial frequency converter adopts the constant voltage-frequency ratio U-f curve carrying out constant torque load frequency control to carry out speed governing usually, although the method can reach the performance of frequency control, but the load curve due to blower-pump load is quadratic curve, its load torque becomes quadratic relationship with the output speed of motor, when frequency control is carried out to it, if adopt constant voltage-frequency ratio U-f curve to carry out speed governing, be just equivalent to high load with small power, loss can be increased owing to increasing excitation.So, during quadratic power load at present for frequency converter band pump and fan, usually adopt the U-f curve of quadratic power, as shown in Figure 1, but due to different motors, water technical data required for the pump different, so its quadratic curve is also and inconsistent.So be necessary to carry out accurate U-f curve determination.

For photovoltaic water pump system, in order to improve generating efficiency, cost-saving, obtain maximum water yield, just must carry out maximal power tracing.In current AC photovoltaic water pump system, conventional maximum power tracking method is all carry out maximal power tracing based on carrying out regulation output power to the adjustment of frequency converter output frequency, the method effect when comparatively low frequency is better, because it is less in the power output corresponding compared with the frequency of one step during low frequency change, tracing control is comparatively accurate, and when higher-frequency, power output corresponding to the frequency due to one step changes greatly, adverse influence will be brought to the precision controlled.

Summary of the invention

The object of this invention is to provide a kind of maximal power tracing of photovoltaic water pump system and the method that U-f curve is combined from optimizing, the efficiency of photovoltaic water pump system can be improved, and the precision of control can be improved.

The technical solution adopted in the present invention is, the method that maximal power tracing and the U-f curve of photovoltaic water pump system are combined from optimizing, when lower frequency, adopts frequency converter output frequency f to control power output P _m, when upper frequency, adopt frequency converter output voltage amplitude U to control power output P _m, changed power corresponding to its unit amplitude is relatively little, just can meticulousr by the output power of frequency converter; Until make water pump trace into the maximum power of photovoltaic panel output.

Feature of the present invention is also:

Adopt frequency converter output frequency to control power output, the relational expression of control is:

$p_m=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^3{n}^3$

Wherein, P _mfor the power output of motor, A _pfor moment coefficient, n is motor speed, and the value of frequency converter output frequency f equals the value of motor speed n.

Frequency converter output voltage amplitude U controls power output P _mfor:

First control frequency converter output frequency f according to frequency converter output voltage amplitude U in quadratic power U-f curve, the frequency converter output frequency f obtained is again to power output P _mcontrol, the relational expression of control is:

$p_m=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^3{n}^3$

Wherein, P _mfor the power output of motor, A _pfor moment coefficient, n is motor speed, and the value of frequency converter output frequency f equals the value of motor speed n.

Control relationship computational process be:

By Electrical Motor volume, when motor belt motor blower-pump load, the load torque T of motor _lwith motor angular velocity ω _rsquare to be directly proportional:

$T_L=A_p\·{\mathrm{\ω}}_r^2---\left(1\right)$

Wherein, A _pfor moment coefficient;

Due to

$n=\frac{60{\mathrm{\ω}}_r}{2\mathrm{\π}}---\left(2\right)$

Wherein, n is motor speed;

Then

${\mathrm{\ω}}_r=\frac{2\mathrm{\π}\·n}{60}---\left(3\right)$

:

$T_L=A_p\·{\left(\frac{2\mathrm{\π}\·n}{60}\right)}^2=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^2\·n^2---\left(4\right)$

The power output P of motor _mwith the angular velocity omega of rotor _rand electromagnetic torque T _erelation as follows:

$T_e=\frac{P_m}{{\mathrm{\ω}}_r}---\left(5\right)$

Then

P _m＝T _e·ω _r(6)

When motor stable operation, load torque T _lwith electromagnetic torque T _eequal, so combine (4), (6) Shi Ke get:

$P_m=A_p\·{\mathrm{\ω}}_r^3---\left(7\right)$

In combination (3), (7) formula, can obtain:

$P_m=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^3{n}^3---\left(8\right).$

The fit procedure of quadratic power U-f curve is:

Step 1, fixing frequency converter output frequency f;

Step 2, disturbance is carried out to frequency converter output voltage amplitude U;

Step 3, detection frequency converter three-phase output current I _a, I _b, I _cvalue, through 3s/2r conversion after obtain real component I _dwith idle component I _q, obtain power factor

Step 4, repeatedly change frequency converter output voltage U amplitude draw different λ values, compare and find out lambda max values;

Step 5, preservation frequency converter output frequency f and the frequency converter output voltage amplitude U corresponding to lambda max values;

Step 6, judge whether frequency converter output frequency f is greater than 50Hz, if do not had, then frequency increases, and forwards step 2 to, if frequency converter output frequency f is greater than 50Hz, then terminates.

The invention has the beneficial effects as follows: in the method that the maximal power tracing of photovoltaic water pump system of the present invention and U-f curve are combined from optimizing, to the matching of U-f curve, frequency converter is made to have minimum loss when being with blower-pump load, obtain the highest power output, realize energy-conservation, and this quadratic power U-f curve is controlled to combine with the maximal power tracing of photovoltaic water pump system, improves the precision controlled, improve generating efficiency.

Accompanying drawing explanation

Fig. 1 is maximal power tracing control frequency change in voltage figure;

Fig. 2 is the load torque T of blower-pump load in the present invention _lwith the schematic diagram of motor speed n;

Fig. 3 is the power output P of motor speed n and motor in the present invention _mschematic diagram;

Fig. 4 is the flow chart of matching quadratic power U-f curve in the present invention;

Fig. 5 is the schematic diagram of power factor λ and frequency converter output voltage amplitude U when frequency converter output frequency f fixes in the present invention;

Fig. 6 is the quadratic power U-f curve chart simulated in the present invention;

Fig. 7 is the curve chart that quadratic power U-f curve of the present invention and maximal power tracing control to combine.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

The method that maximal power tracing and the U-f curve of photovoltaic water pump system of the present invention are combined from optimizing, when lower frequency, adopts frequency converter output frequency f to control power output P _m, when upper frequency, adopt frequency converter output voltage amplitude U to control power output P _m, changed power corresponding to its unit amplitude is relatively little, just can meticulousr by the output power of frequency converter; Until make water pump trace into the maximum power of photovoltaic panel output.

Note: wherein in the present invention comparatively low frequency and higher-frequency with water pump water outlet point in reality for boundary line.

By Electrical Motor volume, when motor belt motor blower-pump load, load torque T _lwith motor angular velocity ω _rsquare to be directly proportional:

$T_L=A_p\·{\mathrm{\ω}}_r^2---\left(1\right)$

Wherein, A _pfor moment coefficient;

Due to

$n=\frac{60{\mathrm{\ω}}_r}{2\mathrm{\π}}---\left(2\right)$

Wherein, n is motor speed;

Then

${\mathrm{\ω}}_r=\frac{2\mathrm{\π}\·n}{60}---\left(3\right)$

:

$T_L=A_p\·{\left(\frac{2\mathrm{\π}\·n}{60}\right)}^2=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^2\·n^2---\left(4\right)$

Obtain as Fig. 2 curve, this curve is ideally, the load torque T of blower-pump load _lwith the graph of a relation of motor speed n.

The power output P of motor _mwith the angular velocity omega of rotor _rand electromagnetic torque T _erelation as follows:

$T_e=\frac{P_m}{{\mathrm{\ω}}_r}---\left(5\right)$

Then

P _m＝T _e·ω _r(6)

When motor stable operation, load torque T _lwith electromagnetic torque T _eequal, so combine (4), (6) Shi Ke get:

$P_m=A_p\·{\mathrm{\ω}}_r^3---\left(7\right)$

In combination (3), (7) formula, can obtain:

$p_m=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^3{n}^3---\left(3\right)$

Obtain the power output P of motor speed n and motor _mgraph of a relation as shown in Figure 3.

So, by above analysis, during for motor belt motor load of the pumps, in order to raise the efficiency, system U-f curve should change quadratic curve into, but in systems in practice, due to the existence of electromagnetic consumable mechanical loss etc., make actual U-f curve can only be approximate quadratic curve, and relevant with the size of type of be with load etc.To the approximating method optimizing quadratic power U-f curve be introduced below, flow chart as shown in Figure 4:

Step 1, fixing frequency converter output frequency f;

Step 2, disturbance is carried out to frequency converter output voltage amplitude U;

Step 3, detection frequency converter three-phase output current I _a, I _b, I _cvalue, through 3s/2r conversion after obtain real component I _dwith idle component I _q, obtain power factor

Step 4, due to when the output frequency of frequency converter is identical with load, power factor will change along with the change of the size of frequency converter output voltage, and time on the quadratic power U-f curve optimized, its power factor is the highest.The output power factor of frequency converter can become large along with the rising of frequency converter output voltage amplitude when low pressure, and when value on the quadratic power U-f curve after the amplitude of frequency converter output voltage is greater than optimization, its output power factor can reduce again, as shown in Figure 5,

Therefore, repeatedly change frequency converter output voltage U amplitude and draw different λ values, compare and find out lambda max values;

Step 5, preservation frequency converter output frequency f and the frequency converter output voltage amplitude U corresponding to lambda max values;

Step 6, judge whether frequency converter output frequency f is greater than 50Hz, if do not had, then frequency converter output frequency f increases, and forwards step 2 to, if frequency converter output frequency f is greater than 50Hz, then terminates.

During according to each change frequency converter output frequency f, the curve that the frequency converter output frequency f of preservation and the frequency converter output voltage amplitude U corresponding to lambda max values draws out is the quadratic power U-f curve after optimization, specifically as shown in Figure 6.

After obtaining quadratic power U-f curve, itself and maximal power tracing can be controlled to combine, improve control precision, concrete execution mode as shown in Figure 7:

Carrying out maximal power tracing when lower frequency can be frequency converter output frequency f disturbance, because its power output P when frequency converter output frequency f changes when lower frequency _mchange less, control precision is higher.When upper frequency, when there is less change in frequency converter output frequency f, its power output P _mchange will be very large, therefore cause power output P _mthe precision controlled is not high, and then when causing upper frequency, the precision of maximal power tracing is not high.And due to when high frequency the excursion of frequency converter output voltage amplitude U comparatively large, and when changing frequency converter output voltage amplitude U, also can change the power output P of frequency converter _m, for this reason, the present invention adopts the maximal power tracing of photovoltaic water pump system and the method that U-f curve is combined from optimizing: during at lower frequency, adopts frequency converter output frequency f to control power output P _m, when upper frequency, when adopting upper frequency, changed power corresponding to its unit amplitude is relatively little, just can meticulousr by the output power of inverter; Until make water pump trace into the maximum power of photovoltaic panel output.

Claims (5)

1. the maximal power tracing of photovoltaic water pump system and the method that U-f curve is combined from optimizing, is characterized in that, when lower frequency, adopts frequency converter output frequency f to control power output P _m, when upper frequency, adopt frequency converter output voltage amplitude U to control power output P _m, changed power corresponding to its unit amplitude is relatively little, just can meticulousr by the output power of frequency converter; Until make water pump trace into the maximum power of photovoltaic panel output.

2. the maximal power tracing of photovoltaic water pump system according to claim 1 and the method that U-f curve is combined from optimizing, is characterized in that, described employing frequency converter output frequency controls power output, and the relational expression of control is:

$p_m=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^3{n}^3$

Wherein, P _mfor the power output of motor, A _pfor moment coefficient, n is motor speed, and the value of frequency converter output frequency f equals the value of motor speed n.

3. the maximal power tracing of photovoltaic water pump system according to claim 1 and the method that U-f curve is combined from optimizing, is characterized in that, described frequency converter output voltage amplitude U controls power output P _mfor:

First control frequency converter output frequency f according to frequency converter output voltage amplitude U in quadratic power U-f curve, the frequency converter output frequency f obtained is again to power output P _mcontrol, the relational expression of control is:

$p_m=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^3{n}^3$

Wherein, P _mfor the power output of motor, A _pfor moment coefficient, n is motor speed, and the value of frequency converter output frequency f equals the value of motor speed n.

4. maximal power tracing and the method that U-f curve is combined from optimizing of the photovoltaic water pump system according to Claims 2 or 3 any one, is characterized in that, described control relationship computational process be:

By Electrical Motor volume, when motor belt motor blower-pump load, load torque T _lwith motor angular velocity ω _rsquare to be directly proportional:

$T_L=A_p\·{\mathrm{\ω}}_r^2---\left(1\right)$

Wherein, A _pfor moment coefficient;

Due to

$n=\frac{60{\mathrm{\ω}}_r}{2\mathrm{\π}}---\left(2\right)$

Wherein, n is motor speed;

Then

${\mathrm{\ω}}_r=\frac{2\mathrm{\π}\·n}{60}---\left(3\right)$

:

$T_L=A_p\·{\left(\frac{2\mathrm{\π}\·n}{60}\right)}^2=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^2\·n^2---\left(4\right)$

The power output P of motor _mwith the angular velocity omega of rotor _rand electromagnetic torque T _erelation as follows:

$T_e=\frac{P_m}{{\mathrm{\ω}}_r}---\left(5\right)$

Then

P _m＝T _e·ω _r(6)

When motor stable operation, load torque T _lwith electromagnetic torque T _eequal, so combine (4), (6) Shi Ke get:

$P_m=A_p\·{\mathrm{\ω}}_r^3---\left(7\right)$

In combination (3), (7) formula, can obtain:

$p_m=A_p\·{\left(\frac{\mathrm{\π}}{30}\right)}^3{n}^3---\left(8\right).$

5. the maximal power tracing of photovoltaic water pump system according to claim 3 and the method that U-f curve is combined from optimizing, it is characterized in that, the fit procedure of described quadratic power U-f curve is:

Step 1, fixing frequency converter output frequency f;

Step 2, disturbance is carried out to frequency converter output voltage amplitude U;

Step 3, detection frequency converter three-phase output current I _a, I _b, I _cvalue, through 3s/2r conversion after obtain real component I _dwith idle component I _q, obtain power factor

Step 4, repeatedly change frequency converter output voltage U amplitude draw different λ values, compare and find out lambda max values;

Step 5, preservation frequency converter output frequency f and the frequency converter output voltage amplitude U corresponding to lambda max values;

Step 6, judge whether frequency converter output frequency f is greater than 50Hz, if do not had, then frequency increases, and forwards step 2 to, if frequency converter output frequency f is greater than 50Hz, then terminates.