JP7081777B2 - Grid interconnection Inverter system control system design method - Google Patents

Description

The present invention relates to a method for designing a control system for controlling a grid interconnection inverter system including a grid and at least one inverter operating as a power supply source for the grid.

In recent years, DC power output from solar cells, secondary batteries, etc. is converted to 50/60 [Hz] AC power by an inverter, and the converted power is used as a commercial power transmission and distribution system (hereinafter, simply referred to as "system"). The number of non-electric power companies and individuals who supply electricity is increasing rapidly. For this reason, a wide variety of inverters are connected in parallel to today's systems. In this specification, a system including a system and at least one inverter operating as a power supply source for the system is referred to as a "system interconnection inverter system" or simply a "system".

The stability of the system is ensured when suitable control considering stability such as control based on an energy function (for example, Lyapunov function) is applied to each inverter. However, in such controls, some of the degrees of freedom are used to ensure stability. Therefore, the inverter to which such control is applied has a problem that the response to the sinusoidal waveform of the system power is poor.

In order to solve this problem, the present inventors have proposed in Non-Patent Document 1 a method in which the control system of the grid-connected inverter system is composed of a feedback control system and a feed-forward control system. According to this method, it is possible to secure the stability in the feedforward control system using the transfer function H designed by fitting while ensuring the responsiveness in the feedback control system.

Yusuke Nakajima, Toshiji Kato, Kaoru Inoue, "Study of Stabilization Method by Feed Forward Control of Grid-Connected Inverter System", Institute of Electrical Engineers of Japan, Semiconductor Power Conversion / Motor Drive Joint Study Group, SPC-17-014, 2017 Year

However, there are cases where sufficient stability in a frequency band (10 to several k [Hz]) that should be considered in actual use cannot be sufficiently ensured only by applying the above-mentioned conventional method.

The present invention has been made in view of the above circumstances, and the subject thereof is grid interconnection, which can ensure both the responsiveness of the inverter and the stability of the system more reliably than the conventional method. The purpose is to provide a method for designing a control system of an inverter system.

In order to solve the above problems, the design method according to the present invention comprises a feedback control system and a feedback control system for controlling a grid interconnection inverter system including a grid and at least one inverter operating as a power supply source for the grid. It is a method of designing a control system including a feed-forward control system, in which [1] the first step of designing a sinusoidal compensator constituting the feedback control system and [2] the transmission function _Hi of the feed-forward control system (however). , Hi = H ^ _i · _Fi , _i limits the band of the signal transmitted by the secondary or lower main characteristic unit H ^ _i and the main characteristic unit H ^ _i constituting (the number of times this step is executed). A combination of the second step of designing the filter characteristic unit Fi of the second order or lower so that the inverter is passive, and [3 _{] all the transfer functions H i designed} so far in the second step H ₁ + H. If it is determined in the third step of determining whether or not the pass-forwarding of the inverter has been achieved by the feedback control by ₂ + H ₃ + ..., and in the [4] third step, it is transmitted. When the design is completed with the combination of the functions H _i H ₁ + H ₂ + H ₃ + ... as the final transfer function H of the feedback control system, and it is determined that the passivation was not achieved in the third step, it is determined. It includes a fourth step in which the second step is executed again.

The above design method may have a configuration in which the sine wave compensator is designed by the optimum control method in the first step.

Further, the above design method may have a configuration in which the main characteristic unit H ^ _i and the filter characteristic unit _Fi are designed by fitting in the second step. The designed filter characteristic unit _{Fi may be either a primary low-pass filter, a primary high-pass filter, or a secondary band-pass filter, or the primary first filter characteristic unit Fi1 .} And the product _Fi1 and _Fi2 of the first-order second filter characteristic unit _Fi2 may be used.

Further, the above design method determines that the passivation is achieved when the phase of the output admittance Yo of the inverter is within the range of −90 [ _° ] to +90 [°] in the third step. It may have a configuration.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for designing a control system of a grid-connected inverter system, which can ensure both the responsiveness of the inverter and the stability of the system more reliably than the conventional method.

It is a schematic block diagram of the grid interconnection inverter system. It is a circuit diagram which shows an example of the inverter provided in the grid interconnection inverter system shown in FIG. It is an equivalent circuit diagram of the grid interconnection inverter system shown in FIG. It is another equivalent circuit diagram of the grid interconnection inverter system shown in FIG. It is still another equivalent circuit diagram of the grid interconnection inverter system shown in FIG. It is a block diagram of the control system designed by the design method which concerns on this invention. It is a flow chart of the design method which concerns on this invention. It is a graph which shows the amplitude characteristic and the phase characteristic of the output admittance Yo when the output _{admittance Yo of an inverter is Y fb .} It is a graph which shows the amplitude characteristic and the phase characteristic of the output admittance _Yo when the output admittance _Yo of an inverter is Y _fb + Y _ff1 . It is a graph which shows the amplitude characteristic and the phase characteristic of the output admittance _Yo when the output admittance _Yo of an inverter is Y _fb + Y _ff1 + Y _ff2 . It is a graph which shows the linkage point voltage and the inverter output current when the output admittance _Yo of an inverter is Y _fb + Y _ff1 + Y _ff2 .

Hereinafter, the design method of the control system of the grid interconnection inverter system according to the present invention will be described with reference to the accompanying drawings.

(Configuration and stability of grid-connected inverter system)
FIG. 1 shows a grid interconnection inverter system 1 controlled by a control system designed by the design method according to the present invention. As shown in the figure, the grid interconnection inverter system 1 is an inverter (where N is an integer of 1 or more) connected in parallel to the grid 2 having the grid inductor 3 and the grid 2 (where N is an integer of 1 or more). It is equipped with 1 inverter INV ₁ , 2nd inverter INV ₂ , ..., Nth inverter INV _N ). Each of the inverters INV ₁ , INV ₂ , ..., INV _N operates as a power supply source for the system 2.

The potential of the other end when one end of the system 2 is used as a reference is V _s , and the potential of the other end when one of the system interconnection points 4 is used as a reference is V _gc . Further, the inductance of the system inductor 3 is L _s .

As shown in FIG. 2, the first inverter INV ₁ has a DC power supply 5, four switch elements SW ₁ , SW ₂ , SW ₃ , and SW ₄ constituting the single-phase bridge 6, and an output side of the single-phase bridge 6. The LCL type filter 7 provided in the above and the output terminals 11 and 11 connected to the grid interconnection point 4 are provided. The filter 7 is for suppressing harmonics of an output current (current _IL2 described later), and includes a first inductor 8, a second inductor 9, and a capacitor 10. Further, the switch elements SW ₁ , SW ₂ , SW ₃ , and SW ₄ are configured to be turned on / off by a control unit (not shown).

Assuming that the voltage output by the DC power supply 5 is E, the output voltage of the single-phase bridge 6 is uE (however, the command value u is -1≤u≤1). The current flowing through the first inductor 8 is _IL1 , the current flowing through the second inductor 9 is _IL2 , and the voltage generated in the capacitor 10 is v _c . Further, the inductance of the first inductor 8 is L ₁ , the inductance of the second inductor 9 is L ₂ , and the capacitance of the capacitor 10 is C. The current _IL2 is the output current of the first inverter INV ₁ .

The other inverters INV ₂ , ..., Nth inverter INV _N also have the same configuration as the first inverter INV ₁ . However, this is only an example, and the configurations of the inverters INV ₁ , INV ₂ , ..., INV _N may be the same or different.

The grid interconnection inverter system 1 can be represented by the equivalent circuit shown in FIG. That is, each inverter INV ₁ , INV ₂ , ..., INV _N has a current source I _j (however, j = 1, 2, ..., N) and an output admittance Y _j (however, j = 1, 2). , ..., can be represented by the Norton circuit of N). Further, the system side can be represented by a circuit of the system impedance Z _s (however, Z _s = jωL _s ) and the Thevenin circuit of the voltage source V _s .

The equivalent circuit shown in FIG. 3 can be rewritten to the equivalent circuit shown in FIG. However, Yo is the sum of the output _admittances Y ₁ , Y ₂ , ..., Y _N of all inverters INV ₁ , INV ₂ , ..., INV _N. Further, I _o is the sum of the currents output by the currents I ₁ , I ₂ , ..., _IN of all the inverters INV ₁ , INV ₂ , ..., INV _N.

式（１）の右辺の分母にナイキストの安定判別法を適用することにより、「出力アドミタンスＹ_ｏの位相が－９０［°］～＋９０［°］の範囲内に収まっていれば、系統連系インバータシステム１は安定である」との条件を導き出すことができる。なお、系統連系インバータシステム１が安定であることと、系統２に接続されたインバータＩＮＶ_１，ＩＮＶ_２，・・・，ＩＮＶ_Ｎが全体として受動的であることとは等価である。 Here, in the equivalent circuit shown in FIG. 4, the following equation holds in the frequency domain.

By applying Nyquist's stability determination method to the denominator on the right side of equation (1), "if the phase of the output admittance Yo is within the range of -90 [ _° ] to +90 [°], the system interconnection The condition that "the inverter system 1 is stable" can be derived. It should be noted that the stability of the grid-connected inverter system 1 is equivalent to the fact that the inverters INV ₁ , INV ₂ , ..., INV _N connected to the grid 2 are passive as a whole.

ただし、連続系システム行列Ａ_ｃ、連続系入力ベクトルｂ_ｃ、連続系出力ベクトルｃ_ｃおよび連続系外乱ベクトルｈ_ｃは、式（３）の通りである。

(Equation of state of grid interconnection inverter system)
The equation of state in the continuous system of the grid interconnection inverter system 1 shown in FIGS. 1 and 2 is as follows, where x is the state variable.

However, the continuous system matrix A _c , the continuous system input vector b _c , the continuous system output vector c _c , and the continuous system disturbance vector h _c are as shown in Eq. (3).

ただし、離散系システム行列Ａ、離散系入力ベクトルｂ、離散系出力ベクトルｃおよび離散系外乱ベクトルｈは、式（５）の通りである。

When this is discretized by the sampling period T _s [s], the equation (4) is obtained.

However, the discrete system matrix A, the discrete system input vector b, the discrete system output vector c, and the discrete system disturbance vector h are as shown in Eq. (5).

(System interconnection Inverter system control system design method)
The design method according to the present invention is a method of designing a control system for controlling inverters INV ₁ , INV ₂ , ..., INV _N so as to be passive as a whole. The control system designed by the design method according to the present invention is for ensuring the output admittance Y _fb by the feedback control system for ensuring responsiveness and the passivity (that is, the stability of the grid interconnection inverter system 1). The inverters INV ₁ , INV ₂ , ..., INV _N are controlled so that the output admitance Yo is represented by the sum of the output _admitance Y _ff by the feedforward control system of. Therefore, when the present invention is applied, the equivalent circuit of the grid interconnection inverter system 1 is as shown in FIG. In this equivalent circuit, the following equation holds.

Further, the control system designed by the design method according to the present invention is different from the conventional method described in Patent Document 1, and has a plurality of output admittances Y _ff1 , Y _{ff2 ...} , Y _ffM ( However, M controls the inverters INV ₁ , INV ₂ , ..., INV _N so as to be represented by the sum of 2 or more). Therefore, the equation (6) can be rewritten as the equation (7).

FIG. 6 shows a control system designed by the design method according to the present invention. As shown in the figure, this control system is composed of a main circuit section and a digital circuit section. The design method according to the present invention specifically designs the transfer function G and the state feedback coefficient vector f of the sinusoidal compensator constituting the feedback control system and the transfer function H of the feed forward control system among the control systems. .. In addition, _ir in the figure is a sine wave reference waveform. The transfer function G of the sine wave compensator is expressed by the following equation. However, k ₁ and k ₂ in the equation (8) are control gains.

これを整理すると、式（１０）が得られる。

したがって、インバータＩＮＶ_１，ＩＮＶ_２，・・・，ＩＮＶ_Ｎの出力アドミタンスＹ_ｏ、Ｙ_ｆｂおよびＹ_ｆｆは、以下の通りとなる。

In the control system shown in FIG. 6, the following equation of state holds in the frequency domain.

By rearranging this, the equation (10) is obtained.

Therefore, the output admittances _{Yo, Y fb ,} and Y _ff of the inverters INV ₁ , INV ₂ , ..., INV _N are as follows.

As described above, in the control system designed by the design method according to the present invention, the output admittance Y _ff by the feedforward control system is represented by the sum of a plurality of output admittances Y _ff1 , Y _ff2 ..., Y _ffM . Inverters INV ₁ , INV ₂ , ..., INV _N are controlled. Therefore, the transfer function H in the equation (12) can be rewritten as in the equation (13).

In the design method according to the present invention, the transfer function H ₁ in the equation (13) is the second or lower order limiting the band of the signal transmitted by the main characteristic section H ^ ₁ of the second order or lower and the main characteristic section H ^ ₁ . It is composed of the product of the filter characteristic unit _F1 of the above. The same applies to the other transfer functions H ₂ , H ₃ ..., _HM . Therefore, in the control system designed by the design method according to the present invention, the following equation holds. However, i = 1, 2, ..., M.

Here, the main characteristic unit H ^ _i has, for example, the following equation. However, a ₀ , a ₁ , a ₂ , b ₁ , and b ₂ are coefficients determined by fitting.

フィルタ特性部Ｆ_ｉは、１次のローパスフィルタＦ_ｉＬと１次のハイパスフィルタＦ_ｉＨとの積で表される２次のバンドパスフィルタＦ_ｉＬ・Ｆ_ｉＨであってもよい。 Further, the filter characteristic unit _Fi is, for example, a first-order low-pass filter or a first-order high-pass filter having a format as shown in the following equation. However, c ₀ , c ₁ , and d ₁ are coefficients determined by fitting.

The filter characteristic unit _{Fi may be a second-order bandpass filter FiL / FiH represented by the product of a first-order low-pass filter FiL and a first} -order high-pass filter _FiH .

FIG. 7 shows a flow chart of the design method according to the present invention. As shown in the figure, the design method according to the present invention comprises the first step S1 to the sixth step S6.

In the first step S1, the sine wave compensator constituting the feedback control system is designed by a known method such as an optimum control method. More specifically, in the first step S1, the state feedback coefficient vector f and the control gains k ₁ and k ₂ in the equation (8) are determined.

In the second step S2, the variable i is set to 1, which is the initial value.

In the _third step S3, the transfer function H1 of the feedforward control system is designed. More specifically, in the third step S3, the coefficients a ₀ , a ₁ , a included in the main characteristic unit H ^ ₁ so that the inverters INV ₁ , INV ₂ , ..., INV _N are passive as a whole. ₂ , b ₁ , b ₂ are determined by fitting, and the coefficients c ₀ , c ₁ , d ₁ included in the filter characteristic unit F ₁ that partially limits the band of the signal transmitted by the main characteristic unit H ^ ₁ . Is determined by fitting. For example, if there is an element that hinders passivation in the high frequency part of the signal transmitted by the main characteristic part H ^ ₁ , the coefficients c ₀ , c ₁ , d ₁ are set so that the filter characteristic part F ₁ becomes a low-pass filter. If there is an element that hinders passivation in the low frequency part of the signal transmitted by the main characteristic part H ^ ₁ , the coefficients c ₀ , c ₁ , d ₁ so that the filter characteristic part F ₁ becomes a high-pass filter. To determine. Further, when there is an element that hinders passivation in the high frequency portion and the low frequency portion of the signal transmitted by the main characteristic unit H ^ ₁ , the filter characteristic unit F ₁ = F _1L・ F _1H becomes a bandpass filter. The coefficients c ₀ , c ₁ , and d ₁ of F _1L and F _1H are determined.

In the fourth step S4, it is determined by the above-mentioned stability confirmation method whether or not pass-forward control is achieved by feedforward control by the transfer function H ₁ (= H ^ ₁ · F ₁ ). Here, in the combination of the relatively simple main characteristic part H ^ ₁ and the filter characteristic part F1 of the _{second order or less, the inverters INV 1, INV 2 , ...} , INV _N , no matter how the coefficient is selected, Sufficient invoice may not be achieved. In such a case, in the design method according to the present invention, ₁ is added to the variable i to design the transfer function H2 of the feedforward control system (see the fifth step S5 and the third step S3). On the other hand, if the passivation can be achieved, the transfer function H ₁ is set as the final transfer function H, and the design is completed (see the sixth step S6).

If the main characteristic unit H ^ ₁ and the filter characteristic unit F1 designed in the _third step S3 are of higher order than the third order, it is determined that the passivation cannot be achieved in the fourth step S4. It can be prevented to some extent from being done. However, it is not realistic to use the third-order or higher main characteristic unit H ^ ₁ and the filter characteristic unit F ₁ because the calculation in the third step S3 becomes very complicated.

In the fourth step S4 executed for the second time, it is determined whether or not pass-forward control is achieved by the feedforward control by the transfer function H ₁ + H ₂ . Further, in the fourth step S4 executed for the third time, it is determined whether or not the passforwarding is achieved by the feedforward control by the transfer function H ₁ + H ₂ + H ₃ . In this way, in the fourth step S4, it is determined whether or not the _{passforwarding} is achieved by the feedforward control by the combination H ₁ + H ₂ + H ₃ + ... Of all the transfer functions Hi designed so far. ..

The third step S3, the fourth step S4, and the fifth step S5 are repeatedly executed until it is determined in the fourth step S4 that the passivation has been achieved.

(Specific design example)
Subsequently, a specific design example according to the design method according to the present invention will be described. In this example, it is assumed that one inverter (first inverter INV ₁ ) is connected to the system 2. Further, in this example, the circuit parameters of the first inverter INV ₁ and the like are as shown in Table 1.

First, according to the flow shown in FIG. 7, the state feedback coefficient vectors f and the control gains k1 and k2 _are determined by the optimum control method ( _first step S1). The results are shown in Table 2.

FIG. 8 shows the amplitude characteristic and the phase characteristic of the output admittance Yo when the output _{admittance Yo = Y fb (} that is, when Y _ff is not added to Y _fb ). As shown in the figure, the phase of the output admittance _{Yo (= Y fb )} changes abruptly in the vicinity of 50 [Hz] and exceeds 90 [°]. This indicates that the first inverter INV ₁ is not passive. That is, this indicates that the grid interconnection inverter system 1 may not be stable depending on the grid impedance Z _s .

Therefore, in order to correct this, a transmission characteristic H ₁ (= H ^ ₁ · F ₁ ) corresponding to the output admittance Y _ff1 having a characteristic as shown in the equation (17) is designed (third step S3). However, the values of R _d , L _d , and C _d in the equation (17) are set so that the influence of the output admittance Y _ff1 is the largest in the band in question (see Table 3).

The coefficients of the main characteristic section H ^ ₁ and the filter characteristic section F ₁ (low-pass filter) determined by fitting are as shown in Tables 4 and 5.

FIG. 9 shows the amplitude characteristic and the phase characteristic of the output admittance Yo when the output _{admittance Yo} = Y _fb + Y _ff1 . These indicate that there is a band (50-60 [Hz]) for which passivation has not yet been achieved, although it has been greatly improved by adding the output admittance Y _ff1 (4th step). The result of the determination in S4 is "No").

Therefore, in order to achieve passivation in this band, the transmission characteristic H ₂ (= H ^ ₂ · F _2L · F _2H ) corresponding to the output admittance Y _ff2 is designed (second third step S3). Tables 6, 7 and 8 show the coefficients of the main characteristic part H ^ ₂ , the filter characteristic part F _2L (low-pass filter) and the filter characteristic part F _2H (high-pass filter) determined by fitting.

FIG. 10 shows the amplitude characteristic and the phase characteristic of the output admittance _Yo when the output admittance _Yo = Y _fb + Y _ff1 + Y _ff2 . These indicate that passivation could be achieved in all bands by further adding the output admittance Y _ff2 (the result of the determination in the fourth step S4 is “Yes”).

Finally, the transfer function H in the control system shown in FIG. 6 is H ₁ + H ₂ + H ₃ (sixth step S6).

As shown in FIG. 11, the first inverter INV ₁ controlled by the control system designed in this way also exhibits good characteristics in terms of responsiveness.

Although the method for designing the control system of the grid interconnection inverter system according to the present invention has been described above, the present invention is not limited to the above configuration, and it goes without saying that various modifications are included.

1 grid interconnection Inverter system 2 grid 3 grid inductor 4 grid interconnection point 5 DC power supply 6 single-phase bridge 7 filter 8 1st inductor 9 2nd inductor 10 capacitor 11 output terminal INV ₁ , INV ₂ , ..., INV _N Inverter SW ₁ , SW ₂ , SW ₃ , SW ₄ switch

Claims (6)

A method for designing a control system including a feedback control system and a feedforward control system for controlling a grid interconnection inverter system including a grid and at least one inverter operating as a power supply source for the grid.
The first step of designing the sine wave compensator constituting the feedback control system and
The secondary or lower main characteristic unit H ^ _i and the main characteristic unit H constituting the transfer function Hi of the feedforward control system (however, _Hi = H ^ _i · _Fi , _i is the number of executions of this step). The second step of designing the second or lower filter characteristic unit _Fi that limits the band of the signal transmitted by ^ _i so that the inverter is passive, and
In the second step, it is determined whether or not the pass-forwarding of the inverter is achieved by the _feedforward control by the combination H ₁ + H ₂ + H ₃ + ... Of all the transfer functions Hi designed so far. 3 steps and
When it is determined that the passivation has been achieved in the third step, the combination H ₁ + H ₂ + H ₃ + ... Of the transfer function Hi is designed as the final transfer function H of the _feedforward control system. If it is determined that the passivation was not achieved in the third step, the fourth step of re-executing the second step and
A design method characterized by being equipped with. The design method according to claim 1, wherein in the first step, the sine wave compensator is designed by an optimum control method. The design method according to claim 1 or 2, wherein in the second step, the main characteristic unit H ^ _i and the filter characteristic unit _Fi are designed by fitting. The design method according to any one of claims 1 to 3, wherein the filter characteristic unit _Fi is a first-order low-pass filter, a first-order high-pass filter, or a second-order bandpass filter. .. Claims 1 to 3 are characterized in that the filter characteristic unit _Fi is a product _Fi1 and _Fi2 of a primary first filter characteristic unit _Fi1 and a primary second filter characteristic unit _Fi2 . The design method according to any one of the above. The third step is characterized in that it is determined that the passivation is achieved when the phase of the output admittance Yo of the inverter is within the range of −90 [ _° ] to +90 [°]. The design method according to any one of claims 1 to 5.

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