JP2019058026A - Grid-connected system, power generation controller used therefor, and operation method thereof - Google Patents

Abstract

To enable a grid connection with a power conditioner that can perform an optimal efficiency operation for an input of a fluctuating renewable energy and that can execute maximum power point following control of photovoltaic power generation, for a grid-connected system.SOLUTION: There is provided a grid-connected system for converting a shaft power generated by a power converter with a permanent magnet synchronous generator and an inverter, and flowing inversely to a commercial power supply by via a power conditioner, wherein a power generation controller which controls power generation with the inverter is enabled to perform a power control according to a power curve of the power converter so that it can generate a power generation command value according to the number of revolution of the permanent magnet synchronous generator, and wherein the power conditioner is enabled to execute maximum power point following control for a photovoltaic power generation variably controlling the direct current voltage so that the fluctuation range of DC voltage by the maximum power point following control is maintained within a range where the inverter is operable by the power generation controller limiting the power generation command value according to the DC voltage.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for constructing a distributed power generation system using renewable energy as an input and combining a rotating electric machine for power generation and a power conditioner for grid connection.

  Generally, in the case of a grid-connected system in which renewable energy such as potential energy of unused water is collected by a generator and the generated power is reversely flowed by a power conditioner with a grid-connected function, input of fluctuating renewable energy It is necessary to generate power with maximum efficiency and supply stable DC power to the grid-connected power conditioner.

  On the other hand, grid-connected systems using solar cells are widely used, and these power conditioners for photovoltaic power generation have maximum control that constantly changes the voltage of the DC section that is input from the solar cells so that maximum power can be obtained. The power point tracking control (MPPT) function is installed.

  In order to maximize the conversion efficiency of turbines such as wind turbines and water turbines for the input of fluctuating renewable energy, there is a method of variable speed control of the generator by an inverter, which is widely used especially in large wind power generation systems Yes. In this case, there is a problem that the operation of the inverter cannot be continued if the voltage of the direct current section is greatly fluctuated by the MPPT function of the power conditioner.

  For this problem, it is usually necessary to take measures such as stopping the MPPT function of the power conditioner.

  In addition, small wind power generation and small hydropower generation have a configuration in which a three-phase AC output of a generator is once converted into DC by a diode and then connected to a power conditioner for simplification of the system. Also in this case, the change in the DC voltage caused by the MPPT control for sunlight becomes the change in the torque of the generator as it is, and it is impossible to continue the stable power generation operation and to efficiently use the turbine such as the windmill water turbine.

  Further, even when the MPPT function of the power conditioner is stopped, there is a problem that the maximum efficiency operating point of the turbine is fixed, so that it is not possible to cope with fluctuations in input energy.

  Some power conditioners respond to fluctuations in input energy by boosting or lowering a DC voltage rectified by a diode in accordance with the operation state of the turbine.

  There exists patent document 1 as a background of this technical field. In Patent Document 1, in a grid interconnection system in which a plurality of distributed power supply units connected to a DC bus are connected to the grid via a grid interconnection unit, the power generation state of each distributed power supply unit is controlled based on the voltage of the DC bus. A distributed power supply system has been proposed.

JP 2003-339118 A

  The grid interconnection unit in Patent Document 1 does not assume maximum power point tracking control.

  The purpose of the present invention is directed to a grid interconnection system in which power generated by connecting to a grid is reversely flowed to a grid power supply, and at the same time performing optimum efficiency operation of a turbine or the like with respect to fluctuating renewable energy input, An object of the present invention is to provide a grid interconnection system for renewable energy that enables grid interconnection by a power conditioner equipped with maximum power point tracking control for photovoltaic power generation, a power generation controller used therefor, and an operation method thereof.

  In view of the above-described background art, the present invention is, for example, a system in which shaft power generated by a power conversion machine is converted to DC power by a permanent magnet type synchronous generator and an inverter and is reversely flowed to a commercial power supply via a power conditioner. In the interconnection system, the power generation controller that controls the power generation by the inverter is equipped with power generation control based on the power curve of the power conversion machine to generate a power generation command value according to the rotation speed of the permanent magnet synchronous generator and control the power generation amount The power conditioner is equipped with the maximum power point tracking control for photovoltaic power generation that variably controls the DC voltage, and the power generation controller limits the power generation command value according to the DC voltage, so the fluctuation of the DC voltage by the maximum power point tracking control The range is configured to be maintained within a voltage range in which the inverter can operate.

  According to the present invention, using a power conditioner for photovoltaic power generation equipped with a widely used maximum power point tracking control, a grid interconnection system using a generator that inputs variable renewable energy, and power generation used therefor A controller and its operation method can be provided.

1 is a configuration diagram of a grid interconnection system in Embodiment 1. FIG. It is a figure which shows the power curve for electric power generation control of the electric power generation controller in Example 1. FIG. It is a block diagram of the grid connection system by a general solar power generation. It is a figure which shows the characteristic of the output versus voltage of a common solar cell. It is a figure which shows the electric power generation limitation characteristic of the electric power generation controller in Example 1. FIG. It is a flowchart of the electric power generation control process by the electric power generation controller in Example 1. FIG. 3 is a functional block diagram of a power generation controller in Embodiment 1. FIG. It is a block diagram of the grid connection system by the several generator in Example 2. FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a grid interconnection system in the present embodiment. In FIG. 1, input energy _PIN having fluctuations such as renewable energy is converted into shaft power using a power conversion machine 401 such as a water turbine and input to the permanent magnet type synchronous generator 4. The permanent magnet type synchronous generator 4 generates DC power _PGEN by being controlled by the power generation controller 5 with the inverter 6 and supplies power to the power conditioner 2 for grid connection with the DC cable unit 8. The power conditioner 2 converts the DC power P _GEN into AC power equivalent to that of the commercial power source, and reversely _flows the generated power P _LOAD to the system power source 10. This power generation system is a grid interconnection system connected to the grid power supply.

In general, renewable energy fluctuates more than controlled engine generators. For this reason, the permanent magnet synchronous generator 4 is variable-speed controlled by the inverter 6 in order to maximize the conversion efficiency of the power conversion machine 401 with respect to the fluctuation of the input energy _PIN and to continue the stable power generation operation. The method is widely known.

  FIG. 2 shows a power curve 501 that defines the relationship between the power generation output P and the rotational speed N of a typical turbine such as a water turbine. The power generation controller 5 controls the power generation amount for the permanent magnet synchronous generator 4 based on the power curve 501. In FIG. 2, the horizontal axis indicates the rotational speed of the power conversion machine 401 such as a water turbine or the permanent magnet synchronous generator 4, and the vertical axis indicates the shaft power that the power conversion machine 401 can generate with respect to the rotational speed.

  The power generation controller 5 outputs the maximum power that can be extracted from the power conversion machine 401 based on the rotation speed of the power conversion machine 401 or the permanent magnet synchronous generator 4, that is, the power generation amount from the permanent magnet synchronous generator 4 by the inverter 6. I have control.

When the input _PIN is 70%, the power generation amount that can be extracted from the power curve 501 is P _2, and the rotation speed at that time is N ₂ .

That is, the power generation controller 5 limits the power generation amount P _GEN to 70% when the rotational speed decreases to N _{2 as} a result of the power generation control. The result input _{P IN} and _{P GEN} or rotational speed and balance is stabilized in the state of _{N 2.}

In the system shown in FIG. 1, the voltage V _DC of the DC cable unit is controlled by the power conditioner 2, so that a DC current with P _GEN of 70% of the rating flows through the DC cable unit 8.

As a result, even if the voltage V _DC of the DC cable unit 8 varies by the power conditioner 2 and the input _PIN varies, the power conversion machine 401 can always be operated at the operating point on the power curve 501. .

  In a small-scale power generation system, it is desirable to use general-purpose products as much as possible for the equipment used for cost control. Also in the case of this power generation system, the inverter 6 and the power generation controller 5 that control the permanent magnet synchronous generator 4 at a variable speed are assumed to be general-purpose low-voltage inverters. However, these general-purpose inverter products are premised on the supply of stable commercial power, and there is a limit on the allowable range of the internal DC voltage after full-wave rectification by a diode. That is, the fluctuation range of the DC voltage of the DC cable portion 8 in FIG. 1 is limited by the allowable fluctuation range of the DC voltage of the inverter 6.

FIG. 3 shows a configuration of a general photovoltaic power generation system. In FIG. 3, the solar radiation is input energy _PIN , which is converted into DC power P _DC by the solar cell array 201 and input to the power conditioner 2 via the DC cable unit 8. The power conditioner 2 converts the DC power P _DC into AC power equivalent to that of the commercial power source and reversely _flows the generated power P _LOAD to the system power source 10. This power generation system is also a grid interconnection system connected to the grid power supply.

The solar cell has the characteristics of DC power output P _PV and DC voltage _VDC shown in FIG. In FIG. 4, the direct current voltage V _DC from which the maximum power P _PV can be extracted differs depending on the varying solar radiation intensity G. For example, when the solar radiation intensity is G ₁ , the direct current voltage is increased to V ₁ and then the solar radiation intensity increases. in the event of a G ₃ Te, it is necessary to move the DC voltage V _3.

This control is realized by controlling the DC voltage _VDC of the DC cable unit 8 by the maximum power point tracking control (MPPT) of the power conditioner 2 of FIG.

In general, this MPPT control detects P _LOAD (at t ₁ ) at a certain time point t ₁ , then increases or decreases the DC voltage value by about 1 to several volts, and then P again at t ₁ + Δt after a short time. _This is a hill climb method in which _LOAD (at t ₁ + Δt) is detected and compared with the previous value to determine whether to increase or decrease the DC voltage next time. By continuing this, the maximum power points A to C of the characteristic curves 301 to 303 shown in FIG. 4 are always searched. By continuously executing this operation, the solar radiation intensity G is allowed to follow.

In other words, the power conditioner 2 for photovoltaic power generation is controlled to vary the voltage _VDC of the DC cable unit 8 in order to always search for the maximum power point.

Here, in order to realize the power generation system shown in FIG. 1 at a low cost, when the power conditioner 2 for photovoltaic power generation, which has been introduced in large quantities in the market, is applied, direct current is controlled by the installed maximum power point tracking control. The voltage _{VDC of the} cable part greatly fluctuates.

In particular, since the voltage range of the solar cell is as wide as 0 to 700 V _DC or about 1000 V _DC , the DC voltage control range by the MPPT of the power conditioner 2 is also very wide, for example, 150 to 700 V _DC .

On the other hand, the DC portion allowable voltage range of the inverter for 200V _AC power reception Examples of general-purpose low-pressure inverter is about 180～380V _DC, the undervoltage trip becomes less 180 V _DC, the overvoltage trip at 380V _DC reaches occur. Since both are protective operations, the inverter stops.

  In the inverter 6 of FIG. 1, when the voltage of the DC cable portion 8 exceeds the above range, a trip occurs, and the power generation control of the permanent magnet type synchronous generator is stopped, and the operation of the power generation system is stopped.

In the present embodiment, the power generation controller 5 monitors the DC voltage V _DC of the DC cable unit 8 and the generated power output P _GEN is determined based on the value of the problem generated by applying the power conditioner 2 for photovoltaic power generation. A method for maintaining the DC voltage _VDC within the operable range of the inverter 6 for the power conditioner 2 by limiting is proposed.

FIG. 5 shows a power generation output automatic limiting characteristic by the power generation controller 5 in this embodiment. The vertical axis represents the limit ratio value Rp with respect to the rated power generation amount, and the maximum is 100% which is the rated power generation amount. The horizontal axis represents the DC voltage _VDC of the DC cable unit 8. An output-voltage characteristic 102 of the solar cell is described on the graph by superimposing an example of generated power versus DC voltage at a solar radiation intensity of the solar cell. For example, the maximum voltage of the solar cell is set at about 700 V _DC , and this is indicated by V ₅ . Output by the power conditioner 2, maximum power point tracking for photovoltaic performs control to find the voltage V ₄ as a maximum.

In this embodiment, the maximum power point tracking control of the power conditioner 2 is used to maintain the DC voltage _VDC in a voltage range in which the inverter 6 can be operated.

In FIG. 5, the lower limit of the allowable voltage range of the inverter 6 is indicated by an undervoltage protection level V _LV , and the upper limit is indicated by an overvoltage protection level V _OV . As shown in the drawing, V _OV is as low as about 380 V _DC with respect to normal V ₅ . Also, V _LV is about 180 V _DC, which is a high value with respect to 0 V.

Automatic limiting characteristic 101 of the power output to be mounted on the power controller 5, when the between V ₁ of the V ₂ 100% not to limit the power output to exceed the below or V ₂ to V _1, as rapidly generator shown in FIG. It is a specification that limits output. The width of V ₁ and V ₂ is set within the operable range of the inverter 6.

For example, when the DC voltage _{V DC} by the control of the power conditioner 2 is reduced from _{V 1} to _{V a,} the power generation controller 5 based on the power curve 501 in FIG. 2, with respect to the command value of the output _{P GEN,} Ra ( P _GEN having a value multiplied by 0 <Ra <1) is output. Accordingly, it is aware of the DC voltage V _DC was controlled to lower the results generated power P _GEN has decreased to the power conditioner 2, induced to return back to V ₁ DC voltage V _DC by the maximum power point tracking control Is.

Similarly, if increased from _{V 2} to _{V b,} induced to return to _{V 2} by multiplying the Rb (0 <Rb <1) with respect to the command value of _{P GEN} limiting the _{P GEN.}

As a result, the direct-current voltage V _DC is maintained in the range of approximately V ₁ to V ₂ as a result, so that V _DC can be maintained at V _LV or more and less than V _OV .

Next, a control flow by the power generation controller 5 will be described. FIG. 6 shows the overall flow of control. In FIG. 6, when the control power supply of the power generation controller 5 is started up, as an initialization process (not shown), an interpolation formula is calculated from parameters that define the rotation speed N and the power generation output P set for generating a power curve. Generate. In step 702, when the rotation of the generator starts, the number of rotations is detected, and the power generation command value P ^* is calculated by using the interpolation formula. In step 703, it detects a DC voltage V _DC, obtains the power generation command value P ^* of the limit percentage value Rp on the basis of this value, instructs actually to the inverter 6 by multiplying the power generation command value P ^* Power An output command value P ^** is calculated. In step 704, the power generation output command value P ^** is set to power generation control.

The relationship between the limiting ratio value Rp and the DC voltage _Vdc is as follows with reference to FIG.
Range of 0 <V _dc <V ₁ : R _P = R (predetermined value)
When V ₁ ≦ V _dc <V ₂ , R _P = f 1 (V _DC ): (function of V _DC )
When V ₂ ≦ Vdc <V3, R _P = f 2 (V _DC ): (function of V _DC )
When V ₃ ≦ Vdc <OV, R _P = R (predetermined value)
It becomes.

  FIG. 7 is a diagram illustrating functional blocks of the power generation controller 5. In FIG. 7, the power generation controller 5 controls the inverter 6 that converts the three-phase AC power generated by the permanent magnet type synchronous generator 4 into DC power that can be supplied to the power conditioner 2. The inverter 6 is controlled by a generator control microcomputer 50 that is a microprocessor. The generator control microcomputer 50 includes a current detection unit 57 that detects a phase current of the permanent magnet type synchronous generator 4 from a current sensor 58 that detects a phase current value of the permanent magnet type synchronous generator 4, and a position / speed estimation calculation unit. 56, a PN voltage detection unit 55 that detects the output voltage value of the inverter 6, a generated power command generation unit 54, a voltage command calculation unit 53, a d / q conversion unit 52, and a PWM control pulse generation unit 51. ing. Since each component is known by general inverter control, its detailed description is omitted. The inverter 6 has a semiconductor switching element. The inverter 6 converts the electric power generated by the permanent magnet synchronous generator 4 into direct current by controlling the semiconductor switching element on / off, and controls the direct current voltage. , Converted into DC power that can be supplied to the power conditioner 2. The generator control microcomputer 50 generates a PWM control signal for on / off control of the semiconductor switching element, and controls the inverter 6.

  As a relationship between the control flow of FIG. 6 and FIG. 7, in step 702, the position (speed) is estimated by the position / speed estimation calculation unit 56 from the current detected by the current detection unit 57, and a power generation command corresponding to the rotation number is obtained. The value is calculated by the generated power command generation unit 54. In step 703, the power generation command value is limited by the PN voltage (DC voltage) detected by the PN voltage detector 55. In step 704, the power generation command value is converted (calculated) into a voltage command by the voltage command calculation unit 53 and set.

By constantly repeating the flow of FIG. 6 at high speed, both the fluctuation of the input energy _{PIN and} the change of the DC voltage _VDC due to the maximum output point tracking control of the power conditioner 2 are supported.
This enables continuous operation of the power generation system.

  In FIG. 1, the permanent magnet type synchronous generator 4, the inverter 6 that drives the permanent magnet type synchronous generator 4, and the power generation controller 5 may be constituted by a rotating electrical machine assembly for power generation.

  As described above, in this embodiment, the power generation controller sets the control target value for the DC voltage value of the DC power output unit, and the generator generates power so that the voltage of the DC unit is always maintained at the target value during the power generation operation. Control power. At the same time, optimal power generation control is performed in consideration of the efficiency of the power conversion machine in response to the changing input energy.

  Furthermore, in order to maintain the DC voltage within the DC voltage range in which the power generation controller can operate, in response to the voltage of the DC unit being controlled by the maximum power point tracking control of the power conditioner for grid connection, A continuous grid-connected system can be operated by restricting the generated power based on a DC voltage value that is a pseudo reproduction of the generated power versus DC voltage characteristics (PV characteristics) of the battery.

  Thereby, the distributed power generation system by the generator which uses the renewable energy which fluctuates as an input can be easily constructed | assembled using the power conditioner for photovoltaic power generation carrying the prevailing maximum electric power point tracking control.

  FIG. 8 is a configuration diagram of a grid interconnection system using a plurality of generators in the present embodiment. 8, components having the same functions as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

In this embodiment, a configuration of a parallel power generation system in which a plurality of power generation systems are connected in parallel at a DC cable portion is shown. In this configuration example, three sets of power generation units are shown, but there are no particular restrictions on the types of input energy, the types of power conversion machines, and the capacities of the generator and the inverter. For example, P _IN1 may be hydropower, P _IN2 may be wind power, and P _IN3 may be steam.

  The power conditioner 2 of this system should just select the capacity | capacitance which can respond | correspond to the maximum total generated electric power of 3 sets.

  However, the number of units on the generator side is not limited, but it is desirable that the number of power conditioners 2 for controlling the DC voltage of the DC cable unit 8 be one.

When connecting a plurality of power conditioners, it is necessary to synchronize the operation of the maximum output point tracking control for controlling the DC voltage _VDC .

  Moreover, it is necessary to unify the DC part allowable voltage range of all inverters connected to the DC cable part.

The feature of this configuration is that the respective power curves of the power conversion machines 611, 621, 631 are set in the power generation controllers 615, 625, 635 with respect to three independent input energies P _IN1 , P _IN2 , P _IN3 . It is possible to perform independent optimum efficiency power generation control.

  On the other hand, in order to correspond to the maximum power output point tracking control of the power conditioner 2 to which the DC power is supplied, all the power generation controllers are equipped with the same power generation output automatic limiting characteristic.

As a result, a plurality of power generation controllers autonomously decentralize the generated power based on the value of the common DC voltage V _DC , so that the DC voltage V _DC of the DC cable unit 8 is changed between the inverters with respect to the power conditioner 2. It is possible to maintain the voltage within the operable range.

  As described above, in this embodiment, even in the case of a distributed power generation system using a plurality of generators, each power generation controller autonomously decentralizes control of each power generation output based on the DC voltage value. Parallel operation with multiple generators is also possible.

  Further, the power generation controller and the grid interconnection power conditioner connected in parallel to the direct current section are not particularly limited in the number of connections, and a plurality of combinations such as a windmill and a water turbine and a combination of a plurality of power conditioners are possible.

  Although the embodiments have been described above, the present invention is not limited to the above-described embodiments, and includes various modifications. Moreover, it is not necessarily limited to what has all the structures demonstrated. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

2: Power conditioner, 4, 614, 624, 634: Permanent magnet synchronous generator, 5,615, 625, 635: Power generation controller, 6,616, 626, 636: Inverter, 8: DC cable section, 10: System 50: generator control microcomputer, 101: automatic output limit characteristic of power generation, 102: output-voltage characteristic of solar battery, 201: solar battery array, 301-303: solar battery PV characteristic curve when solar radiation intensity is G1-3 401, 611, 621, 631: Power conversion machine, 501: Power curve of power conversion machine

Claims (6)

In the grid interconnection system that converts shaft power from the power conversion machine into DC power by a permanent magnet type synchronous generator and inverter and reversely flows to the commercial power supply via the power conditioner,
Power generation control based on the power curve of the power conversion machine is installed in a power generation controller that controls power generation of the permanent magnet synchronous generator by the inverter, and generates a power generation command value according to the rotation speed of the permanent magnet synchronous generator As well as controlling the power generation amount,
The power conditioner is equipped with maximum power point tracking control for photovoltaic power generation that variably controls DC voltage,
The power generation controller has a function of maintaining the DC voltage fluctuation range within the voltage range in which the inverter can operate by limiting the power generation command value according to the DC voltage, by the maximum power point tracking control. System interconnection system characterized by The grid interconnection system according to claim 1,
The power conversion machine, the permanent magnet synchronous generator, the inverter, and a plurality of power generation controllers, and after connecting the DC power generated by each to one DC unit, the maximum power point tracking for the photovoltaic power generation Reverse flow of total power to the system power supply via the power conditioner equipped with control,
Each power generation controller independently performs power generation control based on the power curve of each connected power conversion machine, and the automatic power generation limit characteristic based on the DC voltage value of the DC section is the same for all power generation controllers System interconnection system characterized by mounting The permanent magnet synchronous generator is controlled by the inverter in a grid-connected system that converts shaft power from the power conversion machine to DC power by a permanent magnet synchronous generator and an inverter and flows backward to a commercial power supply via a power conditioner. A power generation controller,
Power generation control based on the power curve of the power conversion machine is installed to generate a power generation command value according to the rotational speed of the permanent magnet synchronous generator, and control the amount of power generation.
The power conditioner is equipped with maximum power point tracking control for photovoltaic power generation that variably controls DC voltage,
The power generation command value is limited according to the DC voltage, and the function of maintaining the DC voltage fluctuation range by the maximum power point tracking control within the voltage range in which the inverter can operate is mounted. Power generation controller. The power generation controller according to claim 3,
The grid interconnection system includes a plurality of the power conversion machine, the permanent magnet synchronous generator, the inverter, and the power generation controller, and connects the DC power generated by each to one DC unit, Reverse the total power to the grid power supply via the power conditioner equipped with maximum power point tracking control for power generation,
Each power generation controller independently performs power generation control based on the power curve of each connected power conversion machine, and the automatic power generation limit characteristic based on the DC voltage value of the DC section is the same for all power generation controllers Power generation controller characterized by being equipped with. It is an operation method in a grid interconnection system in which shaft power generated by a power conversion machine is converted into DC power by a permanent magnet type synchronous generator and an inverter and flows backward to a commercial power supply via a power conditioner,
Power generation control based on the power curve of the power conversion machine is installed in a power generation controller that controls power generation of the permanent magnet synchronous generator by the inverter, and generates a power generation command value according to the rotation speed of the permanent magnet synchronous generator In addition to performing power generation control,
The power conditioner is equipped with maximum power point tracking control for photovoltaic power generation that variably controls DC voltage,
The power generation controller limits the power generation command value according to the DC voltage, thereby maintaining the fluctuation range of the DC voltage by the maximum power point tracking control within a voltage range in which the inverter can operate. how to drive. The driving method according to claim 5,
The grid interconnection system includes a plurality of the power conversion machine, the permanent magnet synchronous generator, the inverter, and the power generation controller, and connects the DC power generated by each to one DC unit, Reverse the total power to the grid power supply via the power conditioner equipped with maximum power point tracking control for power generation,
Each power generation controller independently performs power generation control based on the power curve of each connected power conversion machine, and the power generation automatic limit characteristic based on the DC voltage value of the DC section is the same for all power generation controllers. A driving method characterized by that.

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