JP2022177905A - Current control type inverter and control method for the same - Google Patents

Abstract

To provide an inverter controller and an inverter control method which can practically suppress hunting when a system support function is mounted on a current control type inverter.SOLUTION: A current control type inverter mounted with a system support function and outputting system support power to a power system based on the system support function, includes a compensation control loop for suppressing an influence by a system impedance of the system support power.SELECTED DRAWING: Figure 1

Description

The present invention relates to a current controlled inverter and its control method.

It has been pointed out that the parallel capacity of synchronous generators will decrease due to the expansion of the introduction of renewable energy power sources that are connected to the grid via inverters such as solar and wind power, and that the stability of the grid will decrease. In addition, as a countermeasure, addition of various control functions (system support functions) aimed at supporting grid stabilization to renewable energy power sources is under consideration.

On the other hand, in Non-Patent Documents 1 to 3 below, when various system support functions are implemented in a current-controlled inverter, the control response of the same function continuously vibrates (hunting) depending on the system conditions, and the expected system support There have been reports of cases in which not only is the effect not obtained, but also the system stability is adversely affected.

Shinichiro Maeyama, Keisuke Shirasaki, Hiroyuki Amano. On the instability of pseudo-inertia control that compensates for reduced inertia of a power system. Jun Tamura, Keita Tokumitsu, Hiroyuki Amano. Investigation of influence on frequency control when using storage battery as primary control power. Keisuke Shirasaki, Hiroyuki Amano. Influence of dynamic reactive current control by renewable energy power supply on system stability during main system fault. Report of Central Research Institute of Electric Power Industry R19002. 2020.

By the way, reducing the control gain of the system support function is easily conceivable as a method of suppressing hunting in control response when the system support function is implemented in the current control type inverter. However, in this case, the power system support effect is also reduced at the same time, so there is a trade-off between hunting suppression and power system stabilization. Therefore, the hunting suppression technique that reduces the control gain of the system support function is not preferable.

Reducing the system impedance by installing a new transmission line or the like is also effective as a countermeasure against hunting, but it is difficult in terms of cost and time required for countermeasures. As a countermeasure to suppress hunting in system operation, it is effective not to reduce the number of parallel generators as much as possible and to temporarily avoid work stoppages of system equipment, but there are issues in terms of cost and there is a limit to countermeasures. There is

SUMMARY OF THE INVENTION The present invention has been made in view of the circumstances described above, and aims to provide an inverter control device and an inverter control method that can practically suppress hunting when a system support function is implemented in a current-controlled inverter. and

In order to achieve the above object, in the present invention, as a first solution related to the current control inverter, a system support function is implemented, and current control for outputting system support power to the power system based on the system support function. type inverter with a compensating control loop that suppresses the effect of the grid impedance on the grid support power.

In the present invention, as a second solution related to the current-controlled inverter, in the first solution, the compensation control loop suppresses the effect of its own components in addition to the effect of the system impedance. The transfer function is set as follows.

In the present invention, as a third solution for the current-controlled inverter, in the second solution, the transfer function is set by estimating the system impedance lower than it actually is.

In the present invention, as a fourth solution means related to the current-controlled inverter, in the second solution means, the transfer function is set based on the premises impedance related to the premises itself among the system impedances. adopt means.

In the present invention, as a solution to a control method for a current-controlled inverter, there is provided a control method for a current-controlled inverter that outputs grid support power to a power grid based on a grid support function, wherein a compensation control loop is used to support the grid. A means of suppressing the influence of power system impedance is adopted.

ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the inverter control apparatus and inverter control method which can suppress hunting practically when a system support function is implemented in a current control type inverter.

1 is a block diagram showing a power system in one embodiment of the present invention; FIG. FIG. 3 is a control block diagram showing a control configuration regarding a grid support function of the current controlled inverter according to one embodiment of the present invention; FIG. 3 is a schematic diagram showing system impedance in one embodiment of the present invention; FIG. 4 is a Bode plot of the open-loop transfer function F(s) in one embodiment of the present invention; FIG. 4 is a Bode plot of the closed-loop transfer function K(s) in one embodiment of the invention; FIG. 4 is a Bode plot of open-loop transfer function F(s) showing a combined effect with reduction of control gain in one embodiment of the present invention; FIG. FIG. 5 is a Bode plot of the closed-loop transfer function K(s) showing the combined effect of reducing the control gain in one embodiment of the present invention;

An embodiment of the present invention will be described below with reference to the drawings.
First, an outline of a power system to which a current-controlled inverter according to the present embodiment is applied will be described with reference to FIG.

This power system, as shown in FIG. 1, comprises a renewable energy power supply facility A, an off-site bus B, and an on-site impedance C (including substation equipment). The renewable energy power supply facility A is a power supply facility that generates electric power using well-known renewable energy such as wind power and sunlight, and includes a power generator 1 , a PCS 2 and a premises bus 3 .

The power generation device 1 is a wind power generator that generates electric power using, for example, wind power among well-known renewable energies. The power generator 1 rotates the generator connected to the windmill by rotating the windmill with the wind blowing at the place where the renewable energy power supply equipment A is installed. Such a power generator 1 outputs AC power (generated power) of a predetermined frequency generated by the generator to the PCS 2 .

PCS2 is a current-controlled inverter according to the present embodiment. The PCS 2 is a power conversion device that converts the generated power input from the power generation device 1 into power (on-premises system power) that can be connected to the outside bus B outside the premises. Such a PCS 2 includes an inverter circuit that is a power conversion circuit and a control circuit that controls the inverter circuit.

Here, PCS is commonly known as "Power Conditioning Subsystem". It is also well known that the PCS may implement lineage support functions. The PCS 2 in this embodiment is equipped with a system support function like a well-known PCS, and outputs an injection current to the premises bus 3 for supporting the power system.

That is, the control circuit of PCS2 generates a control signal based on the system support function described above and outputs it to the inverter circuit. The inverter circuit of the PCS 2 generates the injection current based on the control signal input from the control circuit and outputs it to the premises bus line 3 . The injected current is current of active power or reactive power, and is system support power for supporting the power system.

The premises bus 3 is a distribution line laid in the renewable energy power supply facility A. This premises bus 3 is connected to the output end of the PCS 2 as described above. The on-premises bus 3 is also connected to an off-premises bus B via an on-premises impedance C (including substation equipment).

The off-site bus line B is a transmission line laid outside the renewable energy power supply facility A. This off-site bus line B is a part of a power system managed and operated by a general power transmission and distribution business operator, for example.

Next, the control configuration regarding the grid support function will be described in detail with reference to the control block diagram of FIG. That is, the system support function of the PCS 2 includes, as control components, a first adder 4, a second adder 5, a filter element 6, a subtractor 7, a system support element 8, a compensation element 9, a hardware element 10, and a system impedance. An element 11 is provided.

Among these control components, provided by PCS 2 are filter element 6, subtractor 7, system support element 8, compensation element 9 and hardware element 10. FIG. Other than this, the first adder 4, the second adder 5 and the grid impedance element 11 are involved in the control components of the PCS 2 in terms of configuring the grid support function.

The first adder 4 adds the initial state quantity _x0 and the disturbance N, and outputs the result to the second adder 5 as the state quantity x. The initial state quantity _x0 is the initial value of the power state quantity (voltage, phase, etc.) in the power system, and the disturbance N is a noise component that can act on the initial state quantity _x0 .

The second adder 5 adds the state quantity x and the feedback state quantity Δx, and outputs the state quantity X to the filter element 6 . Although the feedback state quantity Δx will be described later, the feedback state quantity Δx is a state quantity that, when added to the state quantity x, destabilizes the system support function in the PCS 2 and induces the hunting phenomenon of the injection current y. .

The filter element 6 is a control component related to the detection filter provided in the PCS 2, and has a transfer function D(s) based on the time constant of the detection filter. This filter element 6 outputs the state quantity _X1 based on the state quantity X and the transfer function D(s) to the subtractor 7 . The subtractor 7 subtracts the state quantity X ₄ from the state quantity X ₁ and outputs the state quantity X ₂ , which is the difference between the state quantity X ₁ and the state quantity X ₄ , to the system support element 8 .

The grid support element 8 is the master control element of the grid support function and has a transfer function G(s). This system support element 8 is, for example, a well-known PID control element, and outputs state quantity _X3 based on state quantity _X2 and transfer function G(s) to compensation element 9 and hardware element 10 .

The compensating element 9 is a control component that generates a state quantity _X4 that suppresses or eliminates the influence of the feedback state quantity Δx described above, and has a transfer function H(s). That is, the compensating element 9 generates a _state quantity X4 based on the state quantity _X3 and the transfer function H(s), and outputs the state quantity _X4 to the subtractor 7 . This state quantity _X4 functions as a compensation quantity for suppressing or eliminating the influence of the feedback state quantity Δx.

Such compensating element 9 forms a feedback control loop for system support element 8 as shown. A feedback control loop based on this compensating element 9 functions as a compensating control loop for suppressing or eliminating the influence of the feedback state quantity Δx. That is, the transfer function H(s) in the compensation control loop is a compensation transfer function set to suppress or eliminate the influence of the feedback state quantity Δx.

A hardware element 10 is a control component resulting from the hardware configuration of PCS2 and has a transfer function W(s). This hardware element 10 outputs the injection current y set based on the state quantity _X3 and the transfer function W(s) to the system impedance element 11 and the post-stage control element of PCS2. The controller of PCS2 generates a control signal for the inverter circuit based on this injected current y.

In this embodiment, the impedance of the electric power system to which the output end of the PCS 2 is connected, that is, the total impedance of the impedance of the on-premises bus 3, the impedance of the off-premises bus B, and the impedance of the main system is referred to as the system impedance.

This system impedance is classified into an on-site impedance _Z1 and an external impedance _Z2 , as shown in FIG. The premises impedance Z ₁ is the premises impedance related to the premises itself, that is, the complex impedance of the premises wiring and substation equipment, and the external impedance Z ₂ is the impedance other than the premises impedance Z ₁ , that is, the main system side viewed from the outside bus B. is the embedded impedance.

The system impedance element 11 is a control component that indicates the influence of the system impedance on the injected current y and has a transfer function Z(s). The system impedance element 11 outputs the feedback state quantity Δx based on the injection current y and the transfer function Z(s) to the second adder 5 .

Since the injection current y is output from the output end of the PCS 2 to the on-premises bus 3, the on-premises impedance C (including transformer equipment) from the on-premises bus 3 to the off-premises bus B, and the main system connected to the off-premises bus B Affected by external impedance. As a system support function, the PCS 2 outputs an injection current y corresponding to this influence to the premises bus 3 .

The system impedance element 11 described above constitutes a feedback loop for the main control route from the initial state quantity _x0 to the injection current y, as shown. That is, the system support function constitutes a feedback control system between the PCS2 and the power system. The feedback state quantity Δx is a state quantity that destabilizes the feedback control system due to the system impedance.

Next, a method for controlling the current-controlled inverter according to this embodiment will be described in detail with reference to FIGS. 4 to 7 as well.

First, in the control configuration shown in FIG. 2, the object to be compensated by the hunting suppression control by the compensating element 9 is not only the system impedance, but also extends to the components of the PCS2 itself, that is, the detection filter and the hardware components that constitute the PCS2. It is what I did. If the target of compensation for hunting suppression control is composed only of the system impedance, there is no need to consider the filter element 7 and the hardware element 10 .

That is, the control components of the PCS 2 when the compensation target of the hunting suppression control is composed only of the system impedance are the first adder 4, the second adder 5, the subtractor excluding the filter element 6 and the hardware element 10. 7, a system support element 8, a compensation element 9 and a system impedance element 11; The closed loop transfer function for this basic control configuration is then given by equation (1) below.

In this closed-loop transfer function, the transfer function H(s) of the compensating element 9 and the transfer function Z(s) of the system impedance element 11 have a differential relationship. That is, the equation (1) is such that when both are set equal, the influence of the feedback state quantity Δx is completely compensated, and the injection current y becomes the transfer function G(s) of the system support element 8 and the second adder 5 is given by the product of the state quantity x, which is the output of 5.

The closed-loop transfer function K(s) when the target of compensation for hunting suppression control is extended not only to the system impedance but also to the detection filter and the hardware components constituting PCS2 is given by the following equation (2).

In this case, the transfer function H(s) of the compensating element 9 is the transfer function Z(s) of the system impedance element 11, the transfer function D(s) of the filter element 6, and the transfer function W(s) of the hardware element 10. There is a differential relationship with respect to the product of Therefore, in this case, when the transfer function H(s) and the product of the three transfer functions Z(s), D(s), and W(s) are set equal, the effect of the product feedback state quantity Δx is fully compensated.

The system impedance to be compensated for by the hunting suppression control is a composite impedance of the premises impedance _Z1 and the external impedance _Z2 as shown in FIG. In other words, this system impedance is the impedance looking into the premises side from the inverter interconnection point, which is the connection point between the output end of the PCS 2 and the premises bus 3 .

Such system impedance is a physical quantity that can change according to connection switching of the power system, parallel status of synchronous generators, etc., and it is difficult to grasp the value in real time. If the system impedance is less than the estimated value, it is conceivable that the compensation of the feedback state quantity Δx by the compensating element 9 will be overcompensated. In order to prevent this overcompensation, it is effective to set the transfer function H(s) of the compensating element 9 by estimating the system impedance lower than the actual one.

In order to grasp the influence when the system impedance changes, the feedback loop in FIG. (3).

Here, FIG. 4 shows an example of a Bode diagram of the open-loop transfer function F(s). Also, FIG. 5 shows an example of a Bode diagram of the closed-loop transfer function K(s) described above. That is, these Bode diagrams have an interconnection capacity of 400 MVA, a reference capacity of 1000 MVA, a control gain of 4.0, Z (s) = 1.6, H (s) = n Z (s) D (s) W It is a Bode diagram in the case of (s). Note that n is a variable in increments of 0.25 in the range from 0 to 1.00.

According to the Bode diagram of the open-loop transfer function F(s) shown in FIG. 4, at a frequency where the phase is -180°, the larger the variable n, the more the equivalent gain decreases, and the gain margin increases. It is possible to confirm the tendency of the feedback system to stabilize. When n=0.0, the second term of the denominator in Equation 3 becomes "0", and F(s)=G(s)Z(s)D(s)W(s). Therefore, as the frequency increases, the gain monotonically decreases.

According to the Bode diagram of the gain characteristics for the closed-loop transfer function K(s) shown in FIG. 5, it can be read that the steady gain (gain in the low frequency band) increases as the variable n increases. Dynamic reactive current control is a control that responds to transient voltage deviations. It is conceivable that gain differences have an effect.

However, considering that the dynamic reactive current control normally has a dead band in the range where the voltage deviation is small, and that the Volt-var control is operated separately for the purpose of stabilizing the voltage in the steady state, , it is considered that there is no particular adverse effect due to the difference in the steady-state gain of the dynamic reactive current control.

Further, according to the Bode diagram of the gain characteristics regarding the closed-loop transfer function K(s) in FIG. converges to The fact that the transient gain is equivalent regardless of the value of the variable n means that the amount of reactive current supplied to the voltage drop during the fault is also considered to be equivalent.

When n = 1.0, the second term in the denominator in equation (2) is canceled, and K(s) = -G(s) D(s) W(s). The gain decreases monotonically as the value of .

Furthermore, according to the Bode plot of the phase characteristic for the closed-loop transfer function K(s) in FIG. 5, the stationary phase characteristic and the transient phase characteristic converge to the same value regardless of the value of the variable n. . In particular, if the transient phase characteristics are the same, it is considered that the delay time until the reactive current is supplied to the voltage drop during the accident is also the same.

From such a Bode diagram, as a countermeasure against overcompensation based on the transfer function H(s) due to changes in the system state, the system impedance compensated by the transfer function H(s) should be made smaller than the looking-in impedance. It can be seen that the hunting suppressing effect can be obtained even with However, the smaller the amount of compensation due to the transfer function H(s), the lower the hunting suppression effect.

Here, as described above, the system impedance, that is, the looking-in impedance is the sum of the indoor impedance _Z1 and the external impedance _Z2 as shown in FIG. That is, the premises impedance _Z1 is less than the system impedance. Considering this, it is conceivable that the object of compensation is the premises impedance _Z1 .

This in-plant impedance _Z1 is not only smaller than the system impedance, but also a quantity that can be more easily grasped than the system impedance. Therefore, by limiting the compensation target to the premises impedance _Z1 , it is possible to easily obtain the transfer function H(s) of the compensation loop.

Finally, in the technical problems of the prior art, it has been explained that reducing the control gain of the system support function poses a problem as a method of suppressing hunting in the control response of the system support function. However, by combining with the present invention, it is expected to reduce the trade-off relationship with system stabilization.

The effect of combining the hunting suppression method M1 by reducing the control gain and the hunting suppression method M2 according to the present embodiment was verified. 6 is a Bode plot of the open-loop transfer function F(s) based on the parameter settings in Table 1. FIG. 7 is a Bode plot of the closed-loop transfer function K(s) based on the parameter settings in Table 1. FIG.

According to the Bode diagram of FIG. 6, the transient gains of "no hunting suppression measures" and "suppression method M2" converge to the same value, while the transient gain of "suppression method M1" is decreasing. I understand. This reduction in transient gain means less reactive current supply in dynamic reactive current control where reactive current supply is expected for voltage sags during faults.

Further, according to the Bode diagram of FIG. 7, the gain margin increases at the frequency where the phase is −180° in both the “suppression method M1” and the “suppression method M2” compared to the case of “no hunting suppression measures”. It can be seen that it contributes to the stabilization of the control system.

That is, by combining the hunting suppression method M1 and the hunting suppression method M2, the occurrence of the hunting phenomenon in the control response of the system support function can be effectively suppressed while compensating for the drawback of the hunting suppression method M1, which is the trade-off with system stabilization. can be suppressed.

It should be noted that the present invention is not limited to the above-described embodiments, and for example, the following modifications are conceivable.
(1) In the above embodiment, the case where the present invention is applied to the PCS2 (current control inverter) in the renewable energy power supply equipment A has been described, but the present invention is not limited to this. The present invention is applicable to any current controlled inverter other than a PCS, provided that it has a grid support function.

(2) In the above embodiment, the case where the compensation target of the hunting suppression control is limited to the system impedance and the expansion to the detection filter and the hardware components that constitute the PCS2 in addition to the system impedance have been explained. However, the compensation targets of hunting suppression control are not limited to these detection filters and hardware components.

(3) In the above embodiment, as an example, the compensation target of the hunting suppression control is limited to the premises impedance _Z1 that is smaller than the system impedance, but the present invention is not limited to this. For example, the on-premises impedance _Z1 and part of the external impedance _Z2 (impedance up to the substation) may be subject to compensation.

A Renewable energy power supply facility B Off-site bus bar C On-site impedance (including substation equipment)
1 power generator 2 PCS (current control type inverter)
3 premise bus 4 first adder 5 second adder 6 filter element 7 subtractor 8 system support element 9 compensation element 10 hardware element 11 system impedance element

Claims (5)

A current-controlled inverter in which a grid support function is implemented and which outputs grid support power to a power grid based on the grid support function,
A current-controlled inverter, comprising a compensation control loop that suppresses the influence of system impedance on the system support power. 2. The current-controlled inverter according to claim 1, wherein said compensation control loop has a transfer function set so as to suppress not only the influence of said system impedance but also the influence of its constituent elements. 3. The current control inverter according to claim 2, wherein said transfer function is set by estimating said system impedance lower than it actually is. 3. The current control inverter according to claim 2, wherein said transfer function is set based on a premises impedance related to its own premises among said system impedances. A control method for a current-controlled inverter that outputs grid support power to a power grid based on a grid support function, comprising:
A control method for a current-controlled inverter, comprising: suppressing the influence of system impedance on the system support power by a compensation control loop.

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