JP2016032313A - Inverter apparatus and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter apparatus capable of suppressing variation of the system voltage, by changing the load characteristics of the inverter apparatus connected with a power system for the system voltage, and to provide a control method therefor.SOLUTION: An inverter apparatus 10 includes an inverter 11 connected with a power system 60, a load apparatus 12 connected with the inverter, a measurement unit 13 for measuring the voltage value at the connection point of the power system 60 and inverter 11, and a load characteristics control unit 14. The load characteristics control unit drives the inverter 11 so that the load apparatus 12 is constant power load when the voltage value measured by the measurement unit 13 is in a predetermined range, and drives the inverter 11 so that power consumption reduces monotonously depending on the voltage reduction when the voltage value becomes smaller than the predetermined range.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an inverter device and a control method for the inverter device, and more particularly to an inverter device connected to a power system and a control method therefor.

  Many electrical devices that require power, such as air conditioners and water supply pumps, are driven by an electric motor, and there is no problem if the load on the electric motor is constant. It may continue. When the motor is simply operated at a constant speed using the commercial power frequency against such load fluctuations, it is necessary to adjust the air volume and flow rate according to the load. Excessive energy is discarded by closing, or adjustment is performed while using large energy for starting by frequently starting and stopping the motor.

  For this reason, conventionally, for loads with large load fluctuations such as air conditioners and feed water pumps, the flow rate is controlled by operating the motor at a variable speed using an inverter as disclosed in Patent Documents 1 and 2. By controlling and supplying the necessary flow rate, wasteful power consumption was reduced and a significant energy saving effect was obtained. In addition, when an inverter is connected, the voltage and frequency can be varied. Therefore, the use of the inverter has been promoted in lighting fixtures and electric cookers.

  Even if the power supply voltage fluctuates, the inverter tries to supply power that is commensurate with the load as long as the load does not change. Shows the characteristics. For this reason, with the widespread use of inverters in home appliances, the load power characteristics of the entire home are approaching constant power characteristics.

  On the other hand, in order to realize a low-carbon society in consideration of the global environment, introduction of a large amount of renewable energy using solar power generation (hereinafter simply referred to as PV) has been started. The target for introduction is 28 million kW in 2020 and 53 million kW in 2030. Since the amount of power generated by such renewable energy varies according to natural conditions such as the weather, the more the renewable energy is used in the power system, the more voltage and frequency fluctuations occur in the power system. The possibility increases. For this reason, if appropriate power generation amount control or load control cannot be performed according to the voltage state and frequency state of the power system, the power quality is degraded. That is, a deviation from the reference grid voltage or a deviation from the reference grid frequency occurs.

JP 2003-348892 A JP2013-207925A

  The frequency and voltage fluctuation tolerance of the inverter is large, the frequency is ± 5% (for example, ± 2.5 Hz for a rated 50 Hz), and the voltage is + 6% to −10% (for example, 107.0 to 90.000 for a rated 101 V). 1V). On the other hand, in current Japan, it is necessary to stop the frequency within the range of ± 0.1 to 0.3 Hz and the voltage within the range of 101 ± 6 V in the grid connection of renewable energy. If the range is expanded, the amount of renewable energy grid-connected can be greatly increased. For this reason, inverter conversion of equipment is effective for introducing renewable energy.

  However, as described above, the introduction of PV or the like causes voltage fluctuations in the power system, while the voltage power characteristics in the entire home are approaching the constant power load characteristics. For this reason, when the system voltage decreases, for example, if the load characteristic of household equipment is impedance, the power consumption (active power) decreases as the system voltage decreases. However, in a situation where there are many devices with constant power load characteristics, even if the system voltage decreases, the power consumption does not change unless the user operates to reduce the load power. This increases the possibility of deviation from the reference grid voltage.

  The present invention has been made in view of these circumstances, and by changing the load characteristics with respect to the system voltage of the inverter device connected to the power system, the fluctuation of the system voltage is suppressed and the load continues stable operation. It is an object of the present invention to provide an inverter device that can be used and a control method thereof.

  In order to solve the above-mentioned problem, a first technical means of the present invention is an inverter device having an inverter connected to an electric power system and a load device connected to the inverter, wherein the electric power system and the inverter A measuring unit that measures a voltage value at a connection point; and when the voltage value is within a predetermined range, the load device is driven so that the load device becomes a constant power load, and the voltage value becomes smaller than the predetermined range. And a load characteristic control unit that drives the inverter so that the power consumption of the load device monotonously decreases as the voltage value decreases.

  According to a second technical means, in the first technical means, the load characteristic control unit includes an inverter so that the load device becomes a constant current load or a constant impedance load when the voltage value becomes smaller than the predetermined range. It is characterized by driving.

  According to a third technical means, in the first or second technical means, the load characteristic control unit is configured such that when the voltage value becomes larger than the predetermined range, the load device is rated according to an increase in the voltage value. The inverter is driven so that the power consumption of the load device monotonously increases within a range of power.

  According to a fourth technical means, in any one of the first to third technical means, a natural energy power generation system is connected to the power system to which the inverter is connected via a connection point. It is a thing.

  According to a fifth technical means, in any one of the first to fourth technical means, the predetermined range is narrower than an allowable voltage fluctuation range of the power system.

  A sixth technical means is any one of the first to fifth technical means, wherein the inverter changes the power consumption of the load device by changing an output frequency when the load device is an electric motor. It is characterized by that.

  A seventh technical means is an inverter device control method comprising an inverter connected to an electric power system and a load device connected to the inverter, wherein a voltage value at a connection point between the electric power system and the inverter is a predetermined value. The inverter is driven so that the load device becomes a constant power load when in the range, and when the voltage value becomes smaller than the predetermined range, the power consumption of the load device is reduced according to the decrease in the voltage value. The inverter is driven so as to monotonously decrease.

  According to the present invention, by changing the load characteristics of the inverter device with respect to fluctuations in the system voltage, fluctuations in the system voltage can be effectively suppressed and stable operation of the load can be continued. The possibility of deviation from the reference grid voltage can be reduced.

It is a figure which shows the structural example of the system | strain system containing an example of the inverter apparatus which concerns on this invention. It is a figure which shows an example of the voltage load electric power characteristic of the inverter apparatus which concerns on this invention. It is a figure for demonstrating the relationship which calculates | requires the target output value of an inverter from the system voltage in the inverter apparatus which concerns on this invention. It is a figure for demonstrating typically the relationship between a system voltage power characteristic and a load voltage power characteristic. It is a figure which shows the model circuit used for examination of the system | strain system containing the inverter apparatus of this invention. It is a figure for demonstrating the relationship between the system voltage power characteristic and load voltage power characteristic by the model circuit shown in FIG. It is a figure which shows the response result at the time of producing the model circuit shown in FIG. 5 with a simulator, and performing the electric power supply and extraction | drawer to a system | strain in steps.

  Hereinafter, preferred embodiments of an inverter device and a control method thereof according to the present invention will be described with reference to the drawings. In the following description, the configurations denoted by the same reference numerals in different drawings are the same, and the description thereof may be omitted.

  FIG. 1 is a diagram showing a configuration example of a system system including an example of an inverter device according to the present invention. The grid system 100 supplies power from the substation 20 to the commercial power grid 60 via the transformer 30. The power grid 60 includes a natural energy power generation system 40 such as photovoltaic power generation (PV), and the present invention. The inverter device 10 and the other load device 50 are connected. Further, the electric power generated by the natural energy power generation system 40 is output to the electric power system 60. The output value of the natural energy power generation system 40 is controlled according to the magnitude of the system voltage by a stabilization control device (not shown).

  The inverter device 10 according to the present invention includes an inverter 11 and a load device 12 driven by the inverter 11, and further includes a measuring unit 13 that measures a voltage value at a connection point between the power system 60 and the inverter 11, A load characteristic control unit 14 that changes the load characteristic of the inverter device 10 based on the voltage value measured by the measurement unit 13 is provided. More specifically, the load characteristic control unit 14 drives the inverter 11 so that the load device 12 becomes a constant power load when the voltage value at the connection point between the power system 60 and the inverter 11 is within a predetermined range. When the voltage value becomes smaller than the predetermined range, the inverter is driven so as to have a variable load characteristic in which the power consumption of the load device 12 monotonously decreases with a decrease in voltage.

FIG. 2 is a diagram illustrating an example of voltage load power characteristics of the inverter device according to the present invention, in which the horizontal axis indicates voltage and the vertical axis indicates load power. When the voltage is in the range from the lower limit value V ₁ to the upper limit value V ₂ , the inverter device 10 has a constant power load characteristic of constant load power Pr with a constant load power, and the voltage is lower limit value V. _When it is less than ₁ , the power consumption is such that the power consumption passes through the point b according to the voltage value and decreases on the straight line of the proportionality constant k. When the voltage exceeds the upper limit value V ₂ , as shown by F ₁ (solid line) in FIG. 2, the variable load characteristic is obtained in which the power consumption increases monotonously through the point d as the voltage value increases. If you want to avoid the increase in power consumption as the voltage increases, you can configure it to maintain constant power characteristics as shown by F ₂ (broken line) in FIG. Also good.

When the voltage exceeds the upper limit value V ₂ , the rated power of the load equipment should not be exceeded even when the variable load characteristic indicated by F ₁ (solid line) in FIG. 2 is achieved. Is desirable. That is, when the voltage increases and the power consumption exceeds the rated power of the load device, the load device has a constant power characteristic at the rated power value Pmax as indicated by F ₃ (one-dot chain line). It is desirable not to drive beyond that.

In the inverter device shown in FIG. 2, when the voltage becomes less than V ₁ , the voltage decreases along the straight line of the proportionality constant (slope) k, but the voltage is less than the lower limit value V ₁ of the voltage within the predetermined range. In such a case, the inverter device may be driven so that the power consumption monotonously decreases as the voltage decreases. For example, the inverter device may be configured to have a constant current load characteristic or a constant impedance load characteristic. . Similarly, if the voltage exceeds the upper limit value V ₂ of the voltage of the predetermined range, it may be driven inverter as the inverter device power consumption according to the increase of the voltage increases monotonously. As will be described later, this makes it possible to effectively suppress fluctuations in the system voltage.

The lower limit value V ₁ and the upper limit value V ₂ of the voltage within the predetermined range may be arbitrarily set as long as they are within the allowable voltage range of the power system. For example, the voltage range of the system voltage is 101 ± 6V. Is set to 101V as the reference voltage Vr, and the lower limit value V1 and the upper limit value V2 are set to be values within 6V from the reference voltage Vr. Just keep it. In the following description, in order to simplify the explanation, when the voltage power consumption characteristic shows the characteristic of F ₁ in FIG. 2, that is, when the voltage is out of the predetermined range, the inverter device 10 exhibits the variable load characteristic. The case where it has is demonstrated.

FIG. 3 is a diagram for explaining the relationship for obtaining the target output value of the inverter from the system voltage in the inverter device according to the present invention. The system voltage V, which is the voltage value of the connection point between the power system 60 and the inverter 11 measured by the measuring unit 13, is input to the comparator 14a and compared with the reference voltage Vr. Here, the reference voltage Vr is a center value (a center value between the lower limit value V ₁ and the upper limit value V ₂ ) of a predetermined voltage range in which the inverter device 10 shown in FIG. 2 takes the constant load power Pr. Next, the voltage difference ΔV between the system voltage V and the reference voltage Vr output from the comparator 14a is input to the function calculator 14b.

The function calculator 14b is for calculating the power difference ΔP with respect to the input voltage difference ΔV, and when the voltage difference ΔV is in the range between the voltage value V ₁ ′ and the voltage value V ₂ ′. When zero is output as the power difference ΔP and the voltage difference ΔV is out of the range between the voltage value V ₁ ′ and the voltage value V ₂ ′, a point (V ₁ ′, 0) or ( The value ΔP on the straight line of the gradient a (ΔP / ΔV) is output through V ₂ ', 0). Here, the relationship between the voltage value V ₁ ′ and the voltage value V ₂ ′ and the lower limit value V ₁ and the upper limit value shown in FIG. 2 is the relationship of V ₁ ′ = V ₁ −Vr, V ₂ ′ = V ₂ −Vr. It has become.

The power difference ΔP output from the function calculator 14b is input to the adder 14C, added to the reference power Pr, and output as the target power control value P from the adder 14C. The reference power Pr is a constant load power Pr in a predetermined voltage range between the lower limit value V ₁ and the upper limit value V ₂ shown in FIG. Then, the target power control value P is given to the inverter 11, and the inverter 11 operates so that the output power to the load device 12 becomes the target power control value P. Driving the inverter with the target power control value can be realized by using existing technology.

  For example, when the load device is an electric motor, the inverter 11 controls the rotational speed of the electric motor by changing the output frequency according to the target electric power control value P, and the output electric power to the electric motor becomes the target electric power control value P. Can be. More specifically, the inverter 11 includes an AC-DC converter (inverter unit) that converts AC from the power system into DC, and a DC-AC converter (converter unit) that converts the obtained DC into AC. It is possible to change the output frequency by PWM control in the DC-AC converter according to the target power control value P. Since the rotation speed of the motor is substantially proportional to the input frequency in the case of the induction motor and the power is proportional to the rotation speed, the power consumption of the motor can be controlled by the output frequency control of the inverter 11.

Next, it will be described that the inverter device 10 according to the present invention suppresses fluctuations in the system voltage. FIG. 4 is a diagram for schematically explaining the relationship between the system voltage power characteristic and the load voltage power characteristic. Lines L ₀ , L ₁ , and L ₂ shown in FIG. 4 are lines indicating the system voltage power characteristics of the system 100 shown in FIG. 1, the line L ₀ indicates normal time, and the line L ₁ has a predetermined system voltage. The line L2 indicates when the system voltage has decreased by a predetermined value. The increase or decrease of the system voltage is caused by the increase or decrease of the power from the natural energy power generation system 40 supplied to the power system 60 or the fluctuation of the power supply from the substation 20.

Lines R ₀ , R ₁ , R ₂ shown in FIG. 4 are lines indicating the voltage power load characteristics of the inverter device 10 respectively. When the line R ₀ indicates a constant power load characteristic, the lines R ₁ , R ₂ indicate power consumption. Shows a variable load characteristic that increases and decreases along a straight line with a slope k passing through points b and d according to the voltage value, respectively. In the present embodiment, the load voltage power characteristic of the inverter device 10 indicates that when the system voltage V is within a predetermined voltage range (within the range A between the lower limit value V ₁ and the upper limit value V ₂ shown in FIG. 4), the line R It has a constant power load characteristic indicated by _0, if the lower limit value V ₁ is smaller than has characteristics indicated by the line R _1, if the lower limit value V ₂ less than has the characteristic indicated by the line R _2.

First, when the system 100 is normal, the system voltage V is balanced at the voltage V ₀ at the intersection point a between the system voltage power characteristic line L ₀ and the load voltage power characteristic line R ₀ . When the system voltage decreases and decreases to the line L ₁ of the system voltage power characteristic, the system voltage V decreases from the point a along the line R ₀ to the lower limit value V ₁ of the point b, and further, the system voltage power characteristic It decreases along the line R ₁ until it is balanced at the voltage V ₃ at the intersection c between the line L ₁ and the line R ₁ of the load voltage power characteristic. On the other hand, when the system voltage rises and rises to the line L ₂ of the system voltage power characteristic, the system voltage V rises from the point a along the line R ₀ to the upper limit value V ₂ of the point d, and further The voltage rises along the line R ₂ until the voltage V ₄ at the intersection point e between the voltage power characteristic line L ₂ and the load voltage power characteristic line R ₂ is balanced. As described above, in the inverter device 10 of the present embodiment, when the system voltage power characteristic changes from the line L ₁ to the line L ₂ , the system voltage V varies within the range B from the system voltage V ₃ to V ₄ shown in FIG. Will have a width.

Incidentally, when the inverter device exhibits a constant power load characteristic as in the conventional case, if the system voltage power characteristic changes from the line L ₁ to the line L ₂ , the lines L 1 and L ₂ and the line R ₀ indicating the constant power load characteristic , Each of the intersections f and g has a fluctuation range in a range C formed by the voltages V ₅ and V ₆ . Thus, the inverter device 10 of this embodiment can suppress the fluctuation | variation of a system voltage small compared with the inverter device which has the conventional constant power load characteristic.

  Next, since the model circuit of the system 100 shown in FIG. 1 was created and examined, the result will be described. FIG. 5 is a diagram showing a model circuit used for examining a system system including the inverter device of the present invention. The model circuit 200 is a lumped constant circuit including the generator 101, the line resistance 102, the distributed power source 103, the inverter device 10, and the load device 50. The distributed power source 103 corresponds to the natural energy power generation system 40 of FIG. 1, but in this model circuit, as will be described later, power is supplied to the power system as an element that affects fluctuations in the system voltage, or from the power system. It is handled as receiving power.

In the model circuit of FIG. 5, for simplification, the power consumption (load power) Pin of the inverter device 10 does not set a voltage range having constant power load characteristics, and is constant load when the system voltage is the reference voltage Vr. The load characteristic is such that the power becomes Pr and the power with respect to the voltage changes with the proportional coefficient k. Under this condition, the power consumption Pin of the inverter device 10 can be expressed by Equation 1 when the system voltage is Vline. Equation 1 shows the load voltage-current characteristics of the inverter device 10.
Pin = k × (Vline−Vr) + Pr Equation 1

Further, the power supply voltage by the generator 101 is Vg, the line resistance is Rline, the distributed current input from the distributed power supply 103 to the line is Ipv, the load current flowing into the load device 50 is Iload, and the current flowing into the inverter device 10 is Iin Then, the system voltage Vline and the power consumption Pin can be expressed by Expression 2 and Expression 3, respectively.
Vline = Vg−Rline × (Iload−Ipv + Iin) Equation 2
Pin = Vline × Iin (Formula 3)
By substituting Iin obtained from Equation 2 into Equation 3, Equation 4 is obtained. Equation 4 shows the voltage power characteristics in the model circuit of the grid system.
Pin = (− 1 / Rline) × Vline ² + (Vg / Rline−Iload + Ipv) × Vline
... Formula 4

FIG. 6 is a diagram for explaining the relationship between the system voltage power characteristics and the load voltage power characteristics by the model circuit shown in FIG. When the proportionality coefficient k in Equation 1 is 1.2 (W / V), the reference voltage Vr is 97.7 (v), and the constant load power Pr is 6 (W), the load voltage power characteristic of the inverter device 10 is The load characteristic indicated by the line R ₃ in FIG. 6 is obtained. Next, as the setting values of the parameters in Equation 4, the power supply voltage Vg is 109.7 (V), the line resistance Rline is 54 (Ω), the load current Iload is 0.161 (A), and the distributed current Ipv is 0 ( The relationship between the voltage and power in the case of A) is a characteristic indicated by a curve L ₀ . Furthermore, when the value of the dispersion current Ipv is −0.02 (A) and +0.02 (A), the relationship between the voltage and power is the characteristic curves L ₁ and L ₂ , respectively.

  Here, the reason why the value of the distributed current Ipv is changed to 0, a negative value, and a positive value is to simulate the change in the voltage power characteristic of the model circuit by causing the distributed power source to function as a fluctuation element of the system voltage Vline. Yes, adding 0.02 (A) to the grid as the distributed current Ipv corresponds to supplying about 2 (W) of power to the grid. Further, adding 0.02 (A) to the system as the distributed current Ipv is equivalent to consuming about 2 (W) of power from the system.

As shown in FIG. 6, when the distributed current Ipv is not applied from the distributed power source 103 to the system, the system voltage Vline is 97.7 V, which is the voltage at the intersection point a between the characteristic curve L ₀ and the line R _3, and When the power source 103 subtracts 0.02 (A) from the system as the distributed current Ipv, the system voltage Vline becomes a voltage 97.1 V at the intersection c between the characteristic curve L ₁ and the line R ₃ , and further the dispersion When the power source 103 applied a current of 0.02 (A) as the distributed current Ipv from the system, the system voltage Vline was 98.4 V at the intersection point e between the characteristic curve L ₂ and the line R ₃ . The change width of the system voltage Vline on the variable load characteristic line R ₃ was approximately 1.3V.

Further, if the inverter device 10 is a constant power load whose power consumption does not change even when the system voltage Vline changes, the system voltage Vline is the characteristic curve L ₀ when the distributed current Ipv is not applied from the distributed power source 103 to the system. and it does not change in a voltage of intersection a between the line R ₀ 97.7V, when the distributed power 103 by subtracting a current of 0.02 (a) as a dispersed current Ipv from the system, the system voltage Vline is characteristic When the voltage at the crossing point f between the curve L ₁ and the line R ₀ is 96.6 V and the distributed power source 103 applies a current of 0.02 (A) as the distributed current Ipv from the system, the system voltage Vline is a characteristic. The voltage at the intersection e between the curve L ₂ and the line R ₀ was 98.8V. The change width of the system voltage Vline on the line R ₀ of the constant power load characteristic was approximately 2.2V.

Next, a simulation result when the model circuit shown in FIG. 5 is created using a simulator and the power supply to the system is changed will be described. FIG. 7 is a diagram showing a response result of the system voltage when the model circuit shown in FIG. 5 is created by the simulator, and the power from the distributed power supply 103 is supplied to and extracted from the system in steps. FIG. 7 (A) shows the response result of the system voltage when power 2W is pulled out from the system step by step at the timing t _{0 when} the system voltage is stable at 97.7V, and the thin solid line shows the variable load characteristics. In addition to showing the case, the thick solid line shows the case of constant power characteristics. FIG. 7B shows the response result of the system voltage when power 2W is supplied stepwise to the system at the timing t _{0 when} the system voltage is stable at 97.7 V, and the thin solid line indicates the variable load characteristic. In addition to showing the case, the thick solid line shows the case of constant power characteristics.

  The simulation result shown in FIG. 7 is consistent with the calculation result shown in FIG. 6. According to this embodiment, the variable load characteristic is changed according to the change of the system voltage, rather than driving the inverter device with the constant power load characteristic. By controlling so as to be, it is possible to effectively suppress fluctuations in the system voltage.

DESCRIPTION OF SYMBOLS 10 ... Inverter apparatus, 11 ... Inverter, 12 ... Load apparatus, 13 ... Measuring part, 14 ... Load characteristic control part, 20 ... Substation, 30 ... Transformer, 40 ... Natural energy power generation system, 50 ... Load apparatus, 60 ... Power system, 100 ... system, 101 ... generator, 102 ... line resistance, 103 ... distributed power supply, 200 ... model circuit.

Claims (7)

  An inverter device having an inverter connected to an electric power system and a load device connected to the inverter, a measuring unit for measuring a voltage value at a connection point between the electric power system and the inverter, and the voltage value being within a predetermined range The inverter is driven so that the load device becomes a constant power load when the load device is within, and when the voltage value becomes smaller than the predetermined range, the power consumption of the load device is reduced according to the decrease in the voltage value. An inverter device comprising a load characteristic control unit that drives the inverter so as to monotonously decrease.   The load characteristic control unit drives the inverter so that the load device becomes a constant current load or a constant impedance load when the voltage value becomes smaller than the predetermined range. Inverter equipment.   The load characteristic control unit is configured such that when the voltage value becomes larger than the predetermined range, the power consumption of the load device monotonously increases within the rated power range of the load device according to the increase of the voltage value. The inverter device according to claim 1, wherein the inverter is driven.   The inverter apparatus according to any one of claims 1 to 3, wherein a natural energy power generation system is connected to the power system to which the inverter is connected via a connection point.   The inverter device according to any one of claims 1 to 4, wherein the predetermined range is narrower than an allowable voltage fluctuation range of the power system.   The said inverter changes the power consumption of the said load apparatus by changing an output frequency when the said load apparatus is an electric motor, The inverter apparatus of any one of Claims 1-5 characterized by the above-mentioned.   An inverter device control method comprising an inverter connected to an electric power system and a load device connected to the inverter, wherein the load value when a voltage value at a connection point between the electric power system and the inverter is within a predetermined range. The inverter is driven so that the device has a constant power load, and when the voltage value becomes smaller than the predetermined range, the inverter so that the power consumption of the load device decreases monotonously according to the decrease in the voltage value. A control method for an inverter device, characterized by driving the inverter.

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