JP2019193494A - Control system design method for grid-connected inverter system - Google Patents

Abstract

To provide a control system design method for a grid-connected inverter system in which both inverter responsiveness and system stability can be ensured more reliably than conventional methods.SOLUTION: A design method according to the present invention includes Step S1 of designing a sine wave compensator constituting a feedback control system, Step S3 of designing a main characteristic part H^that constitutes a transfer function Hof a feedforward control system (where i is the number of executions of this step) and a filter characteristic part Fthat limits the bandwidth of a signal transmitted by the main characteristic part, Step S4 of determining whether an inverter has been made passive by the control based on a combination of H+, H+, and the like of all transfer functions Hdesigned in Step S3, and Steps (S5 and S6) of setting the combination of H+, H+, and the like to be a final transfer function H of the feedforward control system when it is determined in Step S4 that the inverter has been made passive and executing Step S3 again when it is determined that the inverter has not been made passive.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a control system design method for controlling a grid-connected inverter system that includes a grid and at least one inverter that operates as a power supply source for the grid.

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

  When suitable control considering stability such as control based on an energy function (for example, Lyapunov function) is applied to each inverter, the stability of the system is ensured. However, in such control, a part of the degree of freedom is used for ensuring stability. For this reason, the inverter to which such control is applied has a problem that the responsiveness to the sinusoidal waveform of the system power is poor.

  In order to solve this problem, the present inventors have proposed a method of configuring a control system of a grid-connected inverter system by a feedback control system and a feedforward control system in Non-Patent Document 1. According to this method, stability can be ensured in the feedforward control system using the transfer function H designed by fitting while ensuring responsiveness in the feedback control system.

Yusuke Nakajo, Toshiji Kato, Satoshi Inoue, “Study on Stabilization Method by Feedforward Control of Grid-connected Inverter System”, The Institute of Electrical Engineers of Japan, Semiconductor Power Conversion / Motor Drive Joint Study Group, SPC-17-014, 2017 Year

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

  The present invention has been made in view of the above circumstances, and the problem is that it is possible to ensure both the response of the inverter and the stability of the system more reliably than the conventional method. The object is to provide a control system design method for an inverter system.

In order to solve the above problem, a design method according to the present invention includes a feedback control system for controlling a grid-connected inverter system including a grid and at least one inverter that operates as a power supply source for the grid, and A control system design method including a feedforward control system, wherein [1] a first step of designing a sine wave compensator constituting the feedback control system, and [2] a transfer function H _i of the feedforward control system (however, _{, H i = H ^ i ·} F i, i limits the bandwidth of the signal transmitted by the main characteristic portion H ^ _i and main characteristics section H ^ _i of the secondary or less constituting the execution count) of the step A second step of designing the second or lower order filter characteristic part F _{i so} that the inverter is passive, and [3] all transfer functions designed so far in the second step. A third step of determining whether Passivation inverter is achieved by feedforward control by combining _{H 1 + H 2 + H 3} + ··· number H _i, passivation is achieved in [4] Third step If it is determined that the transfer function H _i is combined, the design is finished with the combination H ₁ + H ₂ + H ₃ +... Of the transfer function H _i as the final transfer function H of the feedforward control system, and passivation is achieved in the third step. When it is determined that there is not, a fourth step is included in which the second step is executed again.

  In the first step, the design method may have a configuration in which the sine wave compensator is designed by an optimal control method.

Further, the design method may have a configuration in which the main characteristic portion H ^ _i and the filter characteristic portion F _i are designed by fitting in the second step. The designed filter characteristic unit F _i may be any one of a first-order low-pass filter, a first-order high-pass filter, and a second-order band-pass filter, or a first-order first filter characteristic unit F _i1. And the product F _i1 · F _i2 of the first-order second filter characteristic unit F _i2 .

Moreover, the design method, in the third step, the output admittance Y _o of the inverter phase -90 [°] ~ + 90 determines that passivated if within the range of [°] is achieved, and the You may have a structure.

  According to the present invention, it is possible to provide a design method for a control system of a grid-connected inverter system that can ensure both the response of the inverter and the stability of the system more reliably than the conventional method.

It is a schematic block diagram of a grid connection inverter system. It is a circuit diagram which shows an example of the inverter with which the grid connection inverter system shown in FIG. 1 was equipped. FIG. 2 is an equivalent circuit diagram of the grid interconnection inverter system shown in FIG. 1. It is another equivalent circuit schematic of the grid connection inverter system shown in FIG. FIG. 5 is still another equivalent circuit diagram of the grid interconnection inverter system shown in FIG. 1. It is a block diagram of a control system designed by the design method according to the present invention. It is a flowchart of the design method which concerns on this invention. When the output admittance Y _o of the inverter was set to Y _fb, it is a graph showing the amplitude characteristics and phase characteristics of the output admittance Y _o. When the output admittance _{Y o} of the inverter was set to _Y fb _{+ Y ff1,} is a graph showing the amplitude characteristics and phase characteristics of the output admittance _{Y o.} When the output admittance _{Y o} of the inverter was set to _{Y fb + Y ff1 + Y ff2} , is a graph showing the amplitude characteristics and phase characteristics of the output admittance _{Y o.} When the output admittance _{Y o} of the inverter was set to _{Y fb + Y ff1 + Y ff2} , is a graph showing the association point voltage and the inverter output current.

  Hereinafter, a control system design method for a grid-connected 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-connected inverter system 1 controlled by a control system designed by the design method according to the present invention. As shown in the figure, a grid-connected inverter system 1 includes a grid 2 having a grid inductor 3 and N inverters (where N is an integer equal to or greater than 1) connected in parallel to the grid 2. 1 inverter INV ₁ , second inverter INV ₂ ,..., Nth inverter INV _N ). Each inverter INV ₁ , INV ₂ ,..., INV _N operates as a power supply source for the grid 2.

The potential at the other end when one end of the grid 2 is used as a reference is V _s , and the other potential when one of the grid interconnection points 4 is used as a reference is V _gc . Further, the inductance of the line inductor 3 is _{L s.}

As shown in FIG. 2, the first inverter INV ₁ includes a DC power supply 5, four switch elements SW ₁ , SW ₂ , SW ₃ , SW ₄ constituting the single-phase bridge 6, and the output side of the single-phase bridge 6. And an output terminal 11 connected to the grid connection point 4. The filter 7 is for suppressing harmonics of the output current (current I _L2 described later), and includes a first inductor 8, a second inductor 9, and a capacitor 10. The switch elements _{SW 1, SW 2, SW 3} , SW 4 is turned on / off by a control unit (not shown) is configured to be controlled.

When the voltage output from the DC power supply 5 is E, the output voltage of the single-phase bridge 6 is uE (where the command value u is −1 ≦ u ≦ 1). Current flowing through the first inductor 8 _{I L1,} the current flowing through the second inductor 9 voltage generated in the _{I L2,} capacitor 10 is _{v c.} 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. Current _{I L2} is a first output current of the inverter INV _1.

The other inverters INV ₂ ,..., The N-th inverter INV _N have the same configuration as the first inverter INV ₁ . However, this is merely 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 an equivalent circuit shown in FIG. That is, each of the inverters INV ₁ , INV ₂ ,..., INV _N includes a current source I _j (where j = 1, 2,..., N) and an output admittance Y _j (where j = 1, 2). ,..., N) can be represented by a Norton circuit. Further, the system side can be represented by a Thevenin circuit of system impedance Z _s (where Z _s = jωL _s ) and voltage source V _s .

The equivalent circuit shown in FIG. 3 can be rewritten to the equivalent circuit shown in FIG. However, _{Y o} is the total inverter _{INV 1,} INV 2, · · ·, the output of INV _N admittance _{Y 1,} Y 2, · · ·, is the sum of _{Y N.} Also, _{I o} is the total inverter _{INV 1,} INV 2, · · ·, current _I 1 of the INV _N, I 2, · · ·, which is the sum of the _{currents I N} outputs.

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 is established in the frequency domain.

By applying the stability determination method of Nyquist in the denominator of the right side of the equation (1), if the fit phase "output admittance Y _o is in the range of -90 [°] ~ + 90 [ °], grid-connected The condition that the inverter system 1 is stable can be derived. It is equivalent that the grid-connected inverter system 1 is stable and 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。

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

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 Expression (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 with the sampling period T _s [s], 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 Expression (5).

(Control system design method for grid-connected inverter system)
The design method according to the present invention is a method for designing a control system for controlling the 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 ensures output admittance Y _fb by the feedback control system for ensuring responsiveness and passivity (that is, stability of the grid-connected inverter system 1). The inverters INV ₁ , INV ₂ ,..., INV _N are controlled such that the output admittance Y _o is represented by the sum of the output admittance Y _ff by the feedforward control system. Therefore, when the present invention is applied, an equivalent circuit of the grid interconnection inverter system 1 is as shown in FIG. In this equivalent circuit, the following equation holds.

The control system designed by the design method according to the present invention, unlike the conventional technique described in Patent Document 1, the output admittance _{Y ff} plurality of output admittance _{Y ff1, Y ff2 ···, Y} ffM ( However, the inverters INV ₁ , INV ₂ ,..., INV _N are controlled so as to be represented by the sum of M). Therefore, Equation (6) can be rewritten as 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. In the control method according to the present invention, among these control systems, in particular, the transfer function G and state feedback coefficient vector f of the sine wave compensator constituting the feedback control system and the transfer function H of the feedforward control system are designed. . Incidentally, i _r in the figure, a sinusoidal reference waveform. The transfer function G of the sine wave compensator is expressed by the following equation. However, _k 1, _{k 2} in the formula (8) is a control gain.

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 state equation is established in the frequency domain.

If this is rearranged, formula (10) is obtained.

Therefore, the output admittances Y _o , Y _fb and Y _ff of the inverters INV ₁ , INV ₂ ,..., INV _N are as follows.

As described above, the control system designed by the design method according to the present invention, so that the output admittance _{Y ff} by the feed forward control system has multiple output admittance _{Y ff1, Y} ff2 _···, represented by the sum of _{Y FFM} Inverters INV ₁ , INV ₂ ,..., INV _N are controlled. For this reason, the transfer function H in Formula (12) can be rewritten like Formula (13).

Design method according to the present invention, the formula (13) the transfer function H ₁ secondary below for limiting the bandwidth of the signal transmitted by the main characteristic portion H ^ ₁ and main characteristics section H ^ ₁ secondary below in constituted by the product of the filter characteristic portion F ₁ of the. Other transfer functions _{H 2, H} 3 _···, The same applies to the _{H M.} Therefore, in the control system designed by the design method according to the present invention, the following equation is established. However, i = 1, 2,..., M.

Here, the main characteristic portion H ^ _i has, for example, the following formula. However, a ₀ , a ₁ , a ₂ , b ₁ , 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 portion F _i is, for example, a first-order low-pass filter or a first-order high-pass filter having a form of the following expression. Here, c ₀ , c ₁ , and d ₁ are coefficients determined by fitting.

The filter characteristic unit F _i may be a secondary band-pass filter F _iL · F _iH represented by a product of a primary low-pass filter F _iL and a primary high-pass filter F _iH .

  FIG. 7 shows a flow diagram of the design method according to the present invention. As shown in the figure, the design method according to the present invention includes a first step S1 to a 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 optimal 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 an initial value.

In the third step S3, to design the transfer function H ₁ of the feedforward control system. More specifically, in the third step S3, the coefficients a ₀ , a ₁ , a included in the main characteristic portion H ^ ₁ are set so that the inverters INV ₁ , INV ₂ ,..., INV _N are passive as a whole. _{2, b} 1, and determines by fitting the _{b 2,} the coefficient contained a band of the signal transmitted by the main characteristic portion H ^ ₁ to the filter characteristic portions _{F 1} which partially restricted _{c 0, c 1, d} 1 Is determined by fitting. For example, if there is an element that prevents passivation in the high frequency part of the signal transmitted by the main characteristic part H ^ ₁ , the coefficients c ₀ , c ₁ , and d ₁ are set so that the filter characteristic part F ₁ becomes a low-pass filter. If there is an element that is determined and interferes with 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 are set so that the filter characteristic part F ₁ becomes a high-pass filter. To decide. In addition, when there are elements that prevent passivation in the high-frequency part and low-frequency part of the signal transmitted by the main characteristic part H ^ ₁ , the filter characteristic part F ₁ = F _1L · F _1H is a band-pass filter. Then, 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 whether or not the passivation is achieved by the feedforward control by the transfer function H ₁ (= H ^ ₁ · F ₁ ) by the above-described stability confirmation method. Here, in the relatively simple main characteristic portion H ^ ₁ and the combination of the filter characteristic portion _{F 1} of the second order below, the inverter _{INV 1,} INV 2 be selected how the coefficients, ..., the INV _N There may be cases where sufficient passivation cannot be achieved. In such a case, in the design method according to the present invention, by adding 1 to the variable i, to design the transfer function of H ₂ feed forward control system (see the fifth step S5 and the third step S3). On the other hand, if the passivation could be achieved, the transfer function H ₁ as the final transfer function H, and ends the design (see sixth step S6).

Incidentally, the determination of when the main characteristic portion H ^ ₁ and the filter characteristic portion F ₁ designed at the third step S3 3 or higher order such as the passive reduction in the fourth step S4 is not achieved Can be prevented to some extent. However, 3 the use of the following more main characteristic portion H ^ ₁ and the filter characteristic portions F _1, since the calculation in the third step S3 is very complicated, not realistic.

In the fourth step S4 executed for the second time, it is determined whether or not the passivation 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 passivation is achieved by the feedforward control by the transfer function H ₁ + H ₂ + H ₃ . As described above, in the fourth step S4, it is determined whether or not the passivation is achieved by the feedforward control using the combinations H ₁ + H ₂ + H ₃ +... Of all the transfer functions H _i 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)
Next, a specific design example using 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. 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 vector f and the control gains k ₁ and k ₂ are determined by the optimal control method (first step S1). The results are shown in Table 2.

8, when the output admittance _Y o _{= Y fb (i.e.,} when not adding _{Y ff} the _{Y fb),} represents the amplitude and phase characteristics of the output admittance _{Y o.} As shown in the figure, the phase of the output admittance Y _o (= Y _fb ) suddenly changes in the vicinity of 50 [Hz] and exceeds 90 [°]. This indicates that the first inverter INV ₁ is not passive. In other words, this is, by system impedance Z _s utility interactive inverter system 1 indicates that there may not be stable.

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

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

FIG. 9 shows the amplitude characteristic and phase characteristic of the output admittance Y _o when the output admittance Y _o = Y _fb + Y _ff1 . These indicate that there is a band (50 to 60 [Hz]) that has been greatly improved by adding the output admittance Y _ff1 but has not yet been passivated (fourth step). The result of determination in S4 is “No”).

Therefore, in order to achieve passivation in this band, a transfer 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 portion H ₂ , the filter characteristic portion F _2L (low-pass filter) and the filter characteristic portion F _2H (high-pass filter) determined by fitting.

10, in the case where the output admittance _{Y o = Y fb + Y ff1} + Y ff2, shows the amplitude characteristics and phase characteristics of the output admittance _{Y o.} These indicate that the passivation can be achieved in all the 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 set to 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 exhibits good characteristics with respect to responsiveness.

  As mentioned above, although the design method of the control system of the grid connection inverter system based on this invention was demonstrated, this invention is not limited to said structure, It cannot be overemphasized that various deformation | transformation is included.

1 system interconnection inverter system 2 system 3 system inductor 4 system connection point 5 DC power supply 6 single-phase bridge 7 filter 8 first inductor 9 second inductor 10 capacitor 11 output terminals INV ₁ , INV ₂ ,..., INV _N inverter _{SW 1, SW 2, SW 3} , SW 4 switches

Claims (6)

A control system design method including a feedback control system and a feedforward control system for controlling a grid-connected inverter system including a system and at least one inverter that operates as a power supply source for the system,
A first step of designing a sine wave compensator constituting the feedback control system;
The main characteristic part H ^ _{i of} the second order or less and the main characteristic part H constituting the transfer function H _i (where H _i = H _{i i} F _i , i is the number of executions of this step) of the feedforward control system ^ a second step of designing the inverter to be passive with a second or lower order filter characteristic F _i that limits the bandwidth of the signal transmitted by _i ;
In the second step, it is determined whether or not the inverter has been passivated by the feedforward control using the combinations H ₁ + H ₂ + H ₃ +... Of all the transfer functions H _i designed so far. 3 steps,
If it is determined in the third step that the passivation has been achieved, the combination H ₁ + H ₂ + H ₃ +... Of the transfer function H _i is designed as the final transfer function H of the feedforward control system. And when it is determined in the third step that the passivation has not been achieved, a fourth step for executing the second step again;
A design method characterized by comprising: The design method according to claim 1, wherein in the first step, the sine wave compensator is designed by an optimal control method. The design method according to claim 1 or 2, wherein, in the second step, the main characteristic portion H ^ _i and the filter characteristic portion F _i are designed by fitting. 4. The design method according to claim 1, wherein the filter characteristic portion F _i is a first-order low-pass filter, a first-order high-pass filter, or a second-order band-pass filter. 5. . The filter characteristic section _{F i} is claims 1 to 3, characterized in that the product _F i1 · _{F i2} of the primary first filter characteristic section _{F i1} and a primary of the second filter characteristic section _{F i2} The design method according to any one of the above. Claims in the third step, the phase of the output admittance Y _o of said inverter and judging said passivation is achieved if within the range of -90 [°] ~ + 90 [ °] The design method according to any one of claims 1 to 5.

Images