Power conversion device and control method thereof

Abstract

To provide a power conversion device that can stably operate as a virtual synchronous generator.SOLUTION: A power conversion device includes an inverter that converts input DC power into AC power, and a control device that operates the inverter as a virtual synchronous generator, and the control device controls the inverter using a corrected current command value obtained by adding a correction value that brings a DC voltage input to the inverter closer to a target voltage to a first current command value that contributes to active power output from the inverter.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device and a control method thereof. [Background technology]

[0002] Conventionally, there is known a power conversion device that includes an inverter that converts input DC power into AC power, and a control unit that controls the inverter, the control unit having a synchronous generator simulation calculation unit that executes calculations to simulate a synchronous generator, a DC voltage monitoring unit that monitors the DC voltage input to the inverter, and a mechanical input correction unit that sets a mechanical input setting value corresponding to the mechanical input of the synchronous generator as a parameter value used in the synchronous generator simulation calculation unit according to the DC voltage (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 092877 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned mechanical input correction unit corrects the mechanical input set value input to the synchronous generator simulation calculation unit according to the DC voltage input to the inverter. However, if the DC voltage input to the inverter fluctuates significantly, the correction of the mechanical input set value cannot keep up due to the time constant of the mechanical input correction unit, and the deviation between the DC power input to the inverter and the AC power output from the inverter may increase. As a result, the DC voltage input to the inverter may deviate from the normal value, and the power conversion device may not be able to continue to operate stably.

[0005] The present disclosure provides a power conversion device that can stably operate as a virtual synchronous generator and a control method thereof. [Means for solving the problem]

[0006] The first aspect is An inverter that converts input DC power into AC power; A control device that operates the inverter as a virtual synchronous generator, The control device includes: The power conversion device controls the inverter using a corrected current command value obtained by adding a correction value that brings the DC voltage input to the inverter closer to a target voltage to a first current command value that contributes to the active power output from the inverter.

[0007] A second aspect is the power conversion device of the first aspect, The control device includes: Calculating a compensation power value by multiplying a measurement value of an output voltage from the inverter by the correction value; The frequency of the voltage output from the inverter is controlled using a value obtained by subtracting the compensation power value from the measured value of the active power.

[0008] A third aspect is a power conversion device according to the first or second aspect, The control device applies a dead band in which the correction value is zero when the absolute value of the difference between the DC voltage and the target voltage is equal to or less than a predetermined value, or when the value of the difference is an intermediate value between a first predetermined value and a second predetermined value.

[0009] A fourth aspect is a power conversion device according to any one of the first to third aspects, The control device applies a high-pass filter that attenuates signals having a frequency equal to or lower than a cutoff frequency to the difference between the DC voltage and the target voltage, thereby obtaining the correction value.

[0010] A fifth aspect is a power conversion device according to any one of the first to fourth aspects, The control device includes: A measured value of the output current from the inverter is converted into a d-axis current that contributes to the active power and a q-axis current that contributes to the reactive power output from the inverter, and the d-axis current is set as the first current command value.

[0011] A sixth aspect is the power conversion device of the fifth aspect, The control device includes: deriving a frequency command value for an output voltage from the inverter using the measured value of the active power and the measured value of a frequency of the output voltage from the inverter; deriving an amplitude command value for an output voltage of the inverter using the measured value of the reactive power; A second current command value contributing to the reactive power is derived using the q-axis current, the frequency command value, and the amplitude command value.

[0012] A seventh aspect is the power conversion device of the sixth aspect, The control device includes: An output current command value, which is a command value for an output current from the inverter, is derived using the corrected current command value and the second current command value.

[0013] An eighth aspect is the power conversion device of the seventh aspect, The control device includes: deriving an output voltage command value that is a command value for the output voltage from the inverter using the amplitude command value and a phase command value for the output voltage from the inverter; deriving an output voltage correction value that brings the output current of the inverter closer to the output current command value; The inverter is controlled using a command value obtained by adding the output voltage correction value to the output voltage command value.

[0014] The ninth aspect is A control method for a power conversion device that operates an inverter that converts input DC power into AC power as a virtual synchronous generator, comprising: This is a control method for controlling the inverter using a corrected current command value obtained by adding a correction value that brings the DC voltage input to the inverter closer to a target voltage to a first current command value that contributes to the active power output from the inverter. Effect of the Invention

[0015] According to the present disclosure, stable operation of an inverter operating as a virtual synchronous generator can be ensured. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram illustrating a configuration example of a power conversion device according to an embodiment; [Diagram 2] 1 is a diagram illustrating an example of the configuration of an inverter and a control device in a power conversion device according to an embodiment; [Diagram 3] FIG. 2 is a functional block diagram illustrating an example of a frequency control unit in the control device. [Figure 4] FIG. 2 is a functional block diagram illustrating an example of a voltage amplitude control unit in the control device. [Diagram 5] FIG. 2 is a functional block diagram illustrating an example of an instantaneous voltage command unit in the control device. [Figure 6] FIG. 2 is a functional block diagram showing an example of an instantaneous current command unit in the control device. [Figure 7] FIG. 2 is a functional block diagram showing an example of an instantaneous current control unit in the control device. [Figure 8] FIG. 2 is a functional block diagram illustrating an example of a DC voltage control unit in the control device. [Figure 9] FIG. 13 is a diagram showing a modified example of the functional blocks of the control device. [Figure 10] FIG. 4 is a functional block diagram illustrating an example of a power correction unit in the control device. [Figure 11] FIG. 13 is a functional block diagram showing a first modified example of a DC voltage control unit. [Figure 12] FIG. 13 is a functional block diagram showing a second modified example of the DC voltage control unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The following describes the embodiments.

[0018] First, virtual synchronous generator control that operates an inverter as a virtual synchronous generator will be described. As the number of inverters that supply power generated by utilizing renewable energy such as solar power to the power system increases, the stability of the power system may decrease if the ratio of synchronous generators connected to the power system decreases. The reason for this is that while synchronous generators have the function of maintaining the system frequency by the inertia of the rotating body, conventional inverters that use renewable energy are controlled to follow the system voltage at high speed and do not have the characteristic of independently maintaining the frequency like synchronous generators.

[0019] Therefore, development of "virtual synchronous generator control" that simulates the frequency maintenance action of the rotor of a synchronous generator by controlling an inverter is underway. The pseudo-inertia control of the GFM (Grid Forming) control method simulates the equation of motion of a rotating machine in a control system, generates frequency commands and phase commands, and controls the inverter as a whole to operate as a voltage source rather than a current source.

[0020] The control device for the power conversion device of this embodiment also controls the inverter using the GFM control method as a voltage source rather than a current source, but has a control system that has a current control loop as a minor loop that feeds back the current flowing from the output side of the voltage-type inverter to the filter.

[0021] Next, the power conversion device of this embodiment will be described in detail.

[0022] Fig. 1 is a diagram showing an example of a configuration of a power conversion device according to an embodiment. A power conversion device 2 shown in Fig. 1 is connected to a power system 1. The power system 1 is a power system that supplies AC power generated at a power plant to consumer equipment via a distribution line 10.

[0023] The power conversion device 2 is a device that inputs and outputs electric power to and from the power system 1. The power conversion device 2 includes an inverter 5 that inputs and outputs electric power to and from the power system 1, and a control device 20 that operates the inverter 5 as a virtual synchronous generator.

[0024] The inverter 5 is a device that converts input DC power into AC power. The inverter 5 is, for example, an inverter-based resource (IBR) that converts DC power generated from renewable energy such as solar power into AC power and operates in connection with the power grid 1. The inverter 5 includes a power conversion unit 6, a filter 3, and a switch 4.

[0025] The power conversion unit 6 converts a pulse width modulation signal (PWM pulse signal V PWM ) according to the input DC power P in (e.g., DC power generated from renewable energy) into AC power. The power conversion unit 6 converts the PWM pulse signal V PWM According to the above, the voltage v equivalent to the AC voltage PWM The power conversion unit 6 is connected to the power system 1 via the filter 3 and the switch 4.

[0026] The filter 3 removes harmonic components of the current flowing between the power conversion unit 6 and the power grid 1. The filter 3 includes a filter for filtering the AC current i L is input. The filter 3 outputs the current i L The output current i with the harmonic components removed from out is output to power grid 1.

[0027] The filter 3 is, for example, an LCL filter including a reactor L1, a reactor L2, and a capacitor C. The reactor L1 and the reactor L2 are connected in series with each other. The reactor L1 is connected to the output side of the power conversion unit 6, and the reactor L2 is connected to the power system 1 side.

[0028] One end of the capacitor C is connected between the reactor L1 and the reactor L2. The other end of the capacitor C is connected to a neutral point of the three phases (not shown). The other end of the capacitor C may be grounded. Also, instead of such a Y connection (star connection), a Δ connection (delta connection) may be used.

[0029] Since the reactor L1 is present between the power conversion unit 6 and the capacitor C, a difference voltage between the output voltage of the power conversion unit 6 and the voltage of the capacitor C is generated in the reactor L1. This difference voltage and the impedance of the reactor L1 give the current i L Using this property, the control device 20 determines the voltage v output from the power conversion unit 6. PWM By controlling the current i L can be controlled.

[0030] The switch 4 is connected between the power system 1 and the power conversion unit 6. The switch 4 is sometimes called an interconnection switch.

[0031] When the power system 1 is in a normal state, the switch 4 is on, and the inverter 5 can exchange power with the power system 1. When an abnormality such as a failure occurs in the power system 1, the switch 4 switches from on to off, and the inverter 5 is disconnected from the power system 1. The on / off state of the switch 4 is controlled by, for example, the control device 20.

[0032] The inverter 5 is a device that operates as a virtual synchronous generator by a voltage control method (GFM control method).

[0033] Specifically, the inverter 5 generates an output voltage v at a node N connected to the power distribution line 10. out Frequency f out By controlling the filter 3, the active power P out The device outputs the effective power P out When the value is positive, it is the active power output from the inverter 5 to the power system 1, and when the value is negative, it is the active power input from the power system 1 to the inverter 5.

[0034] 2 is a diagram showing an example of the configuration of an inverter and a control device in a power conversion device according to an embodiment of the present invention, and shows a circuit configuration of an inverter 5 and a functional block of a control device 20.

[0035] The inverter 5 includes a power conversion unit 6, a filter 3, and a switch 4. The power conversion unit 6 includes a capacitor 7 and an inverter circuit 8.

[0036] The capacitor 7 smoothes the DC voltage input from an external device such as a power generation device that generates power using renewable energy such as sunlight, and stores the input energy. dc corresponds to the voltage of the capacitor 7 (capacitor voltage).

[0037] The inverter circuit 8 converts DC power input from an external device such as a power generation device into AC power. The inverter circuit 8 converts the DC voltage v smoothed by the capacitor 7 into AC power. dc The AC voltage V PWM Convert it to and output it.

[0038] The control device 20 operates the inverter 5 as a virtual generator. The functions of the control device 20 are realized by a processor such as a CPU (Central Processing Unit) operating according to a program stored in a memory. The functions of the control device 20 may be realized by a FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The functions of the control device 20 may also be realized by an analog circuit using an operational amplifier or the like.

[0039] The control device 20 includes a frequency control unit 22, a voltage amplitude control unit 23, an instantaneous voltage command unit 31, a dq conversion unit 21, an instantaneous current command unit 25, an inverse dq conversion unit 27, an instantaneous current control unit 28, an adder 29, and a PWM pulse generation unit 30. The control device 20 further includes a DC voltage control unit 32 and an adder 35.

[0040] [Frequency control section] The frequency control unit 22 controls the voltage v output from the inverter circuit 8. PWM The frequency control unit 22 controls the frequency of the voltage v output from the inverter circuit 8. PWMBy controlling the frequency of the inverter, the output voltage v output from the inverter 5 to the power grid 1 is out The frequency control unit 22 controls the frequency of the voltage v output from the inverter circuit 8, thereby realizing pseudo-inertia control based on the equation of motion of the rotating machine. PWM The frequency command value f ref and the voltage v output from the inverter circuit 8 PWM The phase command value θ ref and are derived.

[0041] The frequency control unit 22, for example, determines an effective power command value P ref , active power measurement value P out , frequency measurement value f out and rated frequency setting value f n,ref Based on this, the frequency command value f ref and phase command value θ ref Calculate and output.

[0042] Active power command value P ref is the command value of the active power output from the inverter 5 to the power system 1. The active power measurement value P out is a measurement value of the active power actually output from the inverter 5 to the power system 1. out is the measurement at node N between the filter 3 and the power system 1.

[0043] Frequency measurement value f out is the output voltage v that is actually output from the inverter 5 to the power grid 1. out The frequency measurement value f out is the measurement at node N between the filter 3 and the power system 1.

[0044] Rated frequency setting value f n,ref is the set value of the rated frequency of power system 1. The rated frequency set value f n,ref For example, in Japan, eastern Japan uses 50Hz and western Japan uses 60Hz.

[0045] Fig. 3 is a functional block diagram showing an example of a frequency control section in the control device. The frequency control section 22 shown in Fig. 3 is a section that performs frequency control in the GFM control. The frequency control section 22 has adders 22a, 22b, 22f, 22i, and 22k, multipliers 22c, 22e, 22g, 22h, 22j, and 22l, and integrators 22d and 22n.

[0046] In the following description, the unit inertia constant and the unit damping constant are assumed to be H and D, respectively, when the inverter 5 operates as a virtual synchronous generator.

[0047] The adder 22a calculates the active power command value P ref to the measured active power value P out The value obtained by subtracting (P ref -P out ) to the adder 22b.

[0048] The adder 22b receives the input value (P ref -P out The input from the adder 22k is subtracted from the sum of the two, and the result is output to the multiplier 22c.

[0049] The multiplier 22c multiplies the input value from the adder 22b by 1 / (2H) and outputs the result to the integrator 22d (H is a unit inertia constant).

[0050] The integrator 22d integrates the input value from the multiplier 22c and outputs the result to the multiplier 22l.

[0051] The multiplier 22e multiplies the output voltage v out The frequency measurement value f out The rated frequency setting value f of inverter 5 n The output value of the multiplier 22e is the output voltage v out The frequency measurement value f out The rated frequency setting value f n This is a value converted into a unit.

[0052] The adder 22f outputs a value obtained by subtracting the input value from the multiplier 22e from the input value from the integrator 22d to the multiplier 22g.

[0053] The multiplier 22g multiplies the input value from the adder 22f by a unit damping constant D, and outputs the result to the adder 22k.

[0054] Multiplier 22h is the rated frequency setting value f n,ref The rated frequency setting value f of inverter 5 n The output value of the multiplier 22h is the rated frequency setting value f of the power system 1. n,ref The rated frequency setting value f n This is a value converted into a unit.

[0055] The adder 22i subtracts the input value from the multiplier 22h from the input value from the integrator 22d, and outputs the result to the multiplier 22j.

[0056] The multiplier 22j applies a gain K GOV The value multiplied by the gain K is output to the adder 22k. GOV The rotation speed of the rotor is set to the rated frequency f n,ref The fast governor gain is one of the parameters used to adjust the speed so as to keep the

[0057] The adder 22k outputs a value obtained by adding the input value from the multiplier 22g and the input value from the multiplier 22j to the adder 22b.

[0058] The multiplier 22l multiplies the input value from the integrator 22d by the rated frequency setting value f of the inverter 5. n The output value of the multiplier 22l is the output voltage v output from the inverter 5 to the power grid 1. out The voltage v output from the inverter circuit 8 is controlled so that the frequency of PWM The frequency command value f ref is equivalent to.

[0059] The integrator 22n executes a calculation to integrate the value obtained by multiplying the input value from the multiplier 22l by 2π. By this calculation, the integrator 22n obtains the phase command value θ ref Output.

[0060] [Voltage amplitude control section] In FIG. 2, the voltage amplitude control unit 23 controls the voltage v output from the inverter circuit 8. PWM where v PWM The amplitude of v PWM The voltage amplitude control unit 23 controls the voltage v output from the inverter circuit 8. PWM By controlling the amplitude of the output voltage v output from the inverter 5 to the power grid 1, out The amplitude of the reactive power command value Q ref Reactive power measurement value Q out The voltage amplitude control unit 23 controls the voltage v output from the inverter circuit 8. PWM The amplitude command value V ref Derive:

[0061] The voltage amplitude control unit 23, for example, determines a reactive power command value Q ref , reactive power measurement value Q out and output voltage amplitude command value V out,ref Based on this, the amplitude command value V ref Calculate and output.

[0062] Reactive power command value Q ref is the command value of the reactive power output from the inverter 5 to the power grid 1. The reactive power measurement value Q out is a measurement value of the reactive power actually output from the inverter 5 to the power system 1. The reactive power measurement value Q out is the measurement at node N between the filter 3 and the power system 1.

[0063] Output voltage amplitude command value V out,ref is the output voltage v output from the inverter 5 to the power grid 1. out is the amplitude command value.

[0064] Fig. 4 is a functional block diagram showing an example of a voltage amplitude control section in the control device. Voltage amplitude control section 23 shown in Fig. 4 is a section that performs voltage amplitude control of the GFM control. Voltage amplitude control section 23 has adders 23a, 23e, and 23f, multipliers 23b and 23c, an integrator 23d, and a limiting section 23g.

[0065] The adder 23a calculates the reactive power command value Q ref to reactive power measurement value Q out The value obtained by subtracting 1 from 2 is output to the multiplier 23b and the multiplier 23c.

[0066] The multiplier 23b multiplies the input value from the adder 23a by a gain K p,QV The value multiplied by the gain K is output to the adder 23e. p,QV is the reactive power measurement value Q out and reactive power command value Q ref This is a parameter for proportional control to suppress the difference between the gain K p,QV is, for example, the proportional gain of a PI regulator (proportional-integral regulator) for QV droop control.

[0067] The multiplier 23c multiplies the input value from the adder 23a by a gain K i,QV The value multiplied by the gain K is output to the integrator 23d. i,QV is the reactive power measurement value Q out and reactive power command value Q ref This is a parameter for integral control to suppress the difference between the gain K i,QV is, for example, the integral gain of a PI regulator (proportional-integral regulator) for QV droop control.

[0068] The integrator 23d performs time integration of the input value from the multiplier 23c and outputs the result to the adder 23e.

[0069] The adder 23e adds the input value from the multiplier 23b and the input value from the integrator 23d, and outputs the sum to the adder 23f.

[0070] The adder 23f calculates the input value from the adder 23e and the output voltage v out The amplitude command value Vout,ref The sum of these is output to the limiting unit 23g.

[0071] The limiting unit 23g limits the input value from the adder 23f based on the set upper and lower limit values, and sets the limit value as the amplitude command value V ref The output is as follows:

[0072] The limiting unit 23g is configured to limit the input value from the adder 23f to the lower limit value V ref,LLIM Above the upper limit V ref,ULIM If it is equal to or less than this, the input value from the adder 23f is output as is.

[0073] The limiting unit 23g is configured to limit the input value from the adder 23f to the upper limit value V ref,ULIM If it is greater than V ref,ULIM The limiting unit 23g outputs the lower limit V ref,LLIM If it is smaller than the lower limit V ref,LLIM Output.

[0074] The output value of the limiting unit 23g is the output voltage v out The voltage v output from the inverter circuit 8 is controlled so that the amplitude of PWM The amplitude command value V for controlling the amplitude of ref is equivalent to.

[0075] [Instantaneous voltage command section] In FIG. 2, an instantaneous voltage command unit 31 outputs an amplitude command value V ref and phase command value θ ref Based on this, the output voltage command value v out,ref The output voltage command value v out,ref are command values ​​of three-phase instantaneous voltages output from the inverter 5 to the power system 1.

[0076] Fig. 5 is a functional block diagram showing an example of an instantaneous voltage command unit in the control device. The instantaneous voltage command unit 31 shown in Fig. 5 is a part that performs instantaneous voltage command calculation processing in the GFM control. The instantaneous voltage command unit 31 has adders 31a and 31b, cosine functions 31c, 31d, and 31e, multipliers 31f, 31g, and 31h, and a multiplexer 31i.

[0077] The adder 31a calculates a phase command value θ ref The value obtained by subtracting (2π / 3) from (θ ref -(2π / 3)) is output to the cosine function 31d.

[0078] The adder 31b calculates a phase command value θ ref The sum of (θ ref +(2π / 3)) is output to the cosine function 31e.

[0079] The multiplier 31f multiplies the input value cos(θ ref ) to the amplitude command value V ref The output voltage command value v of phase A is out,ref,a The output is as follows:

[0080] The multiplier 31g multiplies the input value cos(θ ref -(2π / 3)) to the amplitude command value V ref The output voltage command value v of phase B is out,ref,b The output is as follows:

[0081] The multiplier 31h multiplies the input value cos(θ ref +(2π / 3)) to the amplitude command value V ref The output voltage command value v out,ref,c The output is as follows:

[0082] The multiplexer 31i outputs the output voltage command value v out,ref,a ,v out,ref,b ,v out,ref,c These are combined into one signal, and the three-phase output voltage command value v output from the inverter 5 to the power grid 1 is out,refIn this example, the three signals are combined into one signal by the multiplexer 31i to make them easier to handle, but the signals may be sent to the next block as three separate signals without using the multiplexer 31i.

[0083] [dq conversion section] In FIG. 2, the dq conversion unit 21 converts a phase command value θ ref Using the above, the output current measurement value i out The current on the two axes (d-axis current i d,out and q-axis current i q,out ) and output the measured output current value i out is a measured value of the output current actually output from the inverter 5 to the power grid 1.

[0084] d-axis current i d,out is the active current component that contributes to the active power output from the inverter 5 to the power grid 1. The q-axis current i q,out is a reactive current component that contributes to the reactive power output from the inverter 5 to the power grid 1. The d-axis current i d,out and q-axis current i q,out are the frequency command values ​​f ref (The voltage v output from the inverter circuit 8 PWM These are the d-axis and q-axis components in a rotating coordinate system that rotates at an angular frequency corresponding to the frequency command value of

[0085] [Instantaneous current command section] In FIG. 2, the instantaneous current command unit 25 controls the d-axis current i d,out , q-axis current i q,out , frequency command value f ref and the amplitude command value V ref Based on this, the d-axis current command value i d,ref and q-axis current command value i q,ref The d-axis current command value i d,ref and q-axis current command value i q,ref is the current i output from the inverter circuit 8 to the filter 3. LThe d-axis current command value i d,ref is an example of a first current command value, and the current i L is the output current i from inverter 5 to power grid 1 out Since there is no significant deviation from the above, it contributes to the effective power output from the inverter 5 to the power grid 1. q,ref is an example of a second current command value, and the current i L is the output current i from inverter 5 to power grid 1 out Since there is no large deviation between these two, the inverter 5 contributes to the reactive power output from the inverter 5 to the power grid 1.

[0086] Fig. 6 is a functional block diagram showing an example of an instantaneous current command unit in the control device. The instantaneous current command unit 25 shown in Fig. 6 is a part that performs instantaneous current command value calculation processing in the GFM control. The instantaneous current command unit 25 has a multiplier 25f, a multiplier 25g, an adder 25h, a limiting unit 25u, and a limiting unit 25v.

[0087] The limiting unit 25u limits the d-axis current i d,out The d-axis current command value i d,ref The output is as follows:

[0088] The limiting unit 25u limits the d-axis current i d,out is the lower limit i d,ref,LLIM The upper limit value i d,ref,ULIM If the above is true, the d-axis current i d,out is output as is.

[0089] The limiting unit 25u limits the d-axis current i d,out is the upper limit i d,ref,ULIM If it is greater than i, d,ref,ULIM The limiting unit 25u outputs the d-axis current i d,out is the lower limit i d,ref,LLIM If it is smaller than i, d,ref,LLIM Output.

[0090] The multiplier 25f multiplies the frequency command value f ref to gain K Ci The value multiplied by the gain K is output to the multiplier 25g. Ci is a coefficient for calculating the current flowing through the capacitor C of the filter 3.

[0091] The multiplier 25g multiplies the input value from the multiplier 25f by the amplitude command value V ref The product of this multiplication is output to an adder 25h.

[0092] The adder 25h receives the q-axis current i q,out The value obtained by adding this to the input value from the multiplier 25g is output to the limiting unit 25v.

[0093] The limiting unit 25v limits the input value from the adder 25h based on the set upper and lower limits, and sets the limit value as the q-axis current command value i q,ref The output is as follows:

[0094] The limiting unit 25v is configured to limit the input value from the adder 25h to the lower limit value i q,ref,LLIM The upper limit value i q,ref,ULIM If it is equal to or less than this, the input value from the adder 25h is output as is.

[0095] The limiting unit 25v is configured to limit the input value from the adder 25h to the upper limit value i q,ref,ULIM If it is greater than i, q,ref,ULIM The limiting unit 25v outputs the lower limit value i q,ref,LLIM If it is smaller than i, q,ref,LLIM Output.

[0096] [Inverse dq transformation section] In FIG. 2, the inverse dq transformation unit 27 converts the current command value of two axes (the d-axis current command value i d,refa and q-axis current command value i q,ref ) is the three-phase output current command value i ref The output current command value i ref is the current i output from the inverter circuit 8 to the filter 3. Lare the command values ​​for the three phases.

[0097] [Instantaneous current control section] In FIG. 2, an instantaneous current control unit 28 controls a current i output from the inverter circuit 8 to the filter 3. L The instantaneous current control unit 28 controls the output current command value i ref The current i output from the inverter circuit 8 to the filter 3 L The instantaneous current control unit 28 performs instantaneous current control to bring the current i L is sampled as an instantaneous current, and the sampled value, the current measurement value i L is the output current command value i ref It can be configured as an ACR (Automatic Current Regulator) that performs feedback control so that the measured current value i L are measured values ​​of instantaneous three-phase currents flowing from the inverter circuit 8 to the reactor L1 of the filter 3.

[0098] The instantaneous current control unit 28 controls the output current command value i ref and current measurement value i L Based on this, the current measurement value i L is the output current command value i ref The output voltage correction value v L,ref The output voltage correction value v L,ref is the output voltage command value v, which is the command value of the three-phase output voltage output from the inverter 5 to the power grid 1. out,ref In order to correct the output voltage command value v out,ref is added by adder 29.

[0099] Fig. 7 is a functional block diagram showing an example of an instantaneous current control section in the control device. The instantaneous current control section 28 shown in Fig. 7 is a section that performs instantaneous current control in the GFM control. The instantaneous current control section 28 has demultiplexers 28a and 28h, adders 28b, 28c, 28e, 28f, 28g, 28i, 28j, and 28k, multipliers 28d, 28l, 28m, and 28n, and a multiplexer 28o.

[0100] The demultiplexer 28a outputs a current measurement value i, which is a measurement value of the filter current flowing from the power conversion unit 6 to the filter 3. L The current measurement value of A phase i L,a , B phase current measurement value i L,b and the current measurement value of C phase i L,c This example is expanded to i L In order to make the signal easier to handle, the signals of each phase are bundled together, and the signals are expanded by the demultiplexer 28a. L These signals may be treated as three separate signals rather than being bundled, in which case demultiplexer 28a is not necessary.

[0101] The adders 28b and 28c calculate the three-phase current measurement values ​​i L,a ,i L,b ,i L,c The sum of these is output to multiplier 28d.

[0102] The multiplier 28d multiplies the three-phase current measurement value i L,a ,i L,b ,i L,c The sum of these is divided by 3 and the result is output to adders 28e, 28f, and 28g.

[0103] The adder 28e calculates the A-phase current measurement value i L,a The adder 28f outputs the value obtained by subtracting the input value from the multiplier 28d from the current measurement value i of the B phase. L,b The adder 28g outputs the value obtained by subtracting the input value from the multiplier 28d from the current measurement value i L,c The multiplier 28c subtracts the input value from the multiplier 28d from the sum and outputs the result to the adder 28k.

[0104] The demultiplexer 28h detects the current i output from the inverter circuit 8 to the filter 3. L The output current command value i ref The output current command value i ref,a ,B-phase output current command value i ref,b and the output current command value i ref,c Expand to.

[0105] The adder 28i calculates the output current command value i ref,a The adder 28j outputs the value obtained by subtracting the input value from the adder 28e from the B-phase output current command value i ref,b The adder 28k outputs the value obtained by subtracting the input value from the adder 28f from the C-phase output current command value i ref,c The adder 28g subtracts the input value from the adder 28c and outputs the result to the multiplier 28n.

[0106] The multiplier 28l applies a gain K ACR The output voltage correction value v of phase A is calculated by multiplying the value by L,ref,a The multiplier 28m outputs the gain K ACR The value multiplied by this is the B phase output voltage correction value v L,ref,b The multiplier 28n outputs the gain K ACR The value multiplied by this is the output voltage correction value v of phase C. L,ref,c The gain K ACR is the measured current value i L and the output current command value i ref This is a parameter for controlling the difference between the gain K ACR is, for example, the P gain (proportional gain) when the ACR control is configured with a P regulator.

[0107] The multiplexer 28o receives the output voltage correction values ​​v of each phase, which are input from the multipliers 28l, 28m, and 28n, respectively. L,ref,a , v L,ref,b ,v L,ref,c These are combined into one signal to produce the three-phase output voltage correction value v L,ref Here, too, similarly to the above case, a configuration without using a multiplexer is possible.

[0108] [Adder] In FIG. 2, an adder 29 calculates an output voltage command value v out,ref to the output voltage correction value v L,refThe value obtained by adding PWM,ref The output is as follows:

[0109] [PWM pulse generation section] In FIG. 2, the PWM pulse generating unit 30 generates a PWM command value v PWM,ref is compared with a carrier signal such as a triangular wave to generate a PWM pulse signal V PWM The pulse width modulation method is not limited to the triangular wave comparison modulation method, and any commonly used pulse width modulation method can be used. It goes without saying that the required number of PWM pulses must be generated depending on the configuration of the inverter circuit 8.

[0110] [DC voltage control section] In FIG. 2, a DC voltage control unit 32 controls a DC voltage v dc The DC voltage control unit 32 controls the target voltage value v dc,ref to DC voltage V dc The DC voltage control unit 32 performs DC voltage control to bring the DC voltage v dc The DC voltage measurement value v dc is the target voltage value v dc,ref It can be configured as an AVR (Automatic Voltage Regulator) that performs feedback control to match the

[0111] The DC voltage control unit 32 detects the DC voltage measurement value v dc and the target voltage value v dc,ref Based on this, the DC voltage measurement value v dc is the target voltage value v dc,ref The d-axis current correction value i dc,ref The d-axis current correction value i dc,ref is the d-axis current command value i generated by the instantaneous current command unit 25. d,ref In order to correct this, the d-axis current command value i d,ref is added by adder 35.

[0112] 8 is a functional block diagram showing an example of a DC voltage control unit in the control device. The DC voltage control unit 32 controls a DC voltage measurement value v dc and the target voltage value v dc,ref A subtractor 32a calculates the difference e between the d-axis current correction value i and the d-axis current correction value i by proportional control that converges the difference e to zero. dc,ref and a proportional control regulator 32b which generates

[0113] [Adder] In FIG. 2, an adder 35 calculates the d-axis current command value i d,ref The d-axis current correction value i dc,ref The value obtained by adding the above is the corrected d-axis current command value i d,ref As a result, the control device 20 outputs the current for operating the inverter 5 as a synchronous generator and the DC voltage measurement value v dc The target voltage value v dc,ref The inverter circuit 8 in the inverter 5 can be controlled so that a current combining the current for bringing the output voltage closer to the reference voltage and the current for bringing the output voltage closer to the reference voltage is output from the inverter 5 to the power grid 1.

[0114] Therefore, the control device 20 of this embodiment determines the d-axis current command value i d,ref , DC voltage measurement value v dc The target voltage value v dc,ref The d-axis current correction value i dc,ref Then, the control device 20 calculates the d-axis current command value i d,refa The inverter circuit 8 of the inverter 5 is controlled using the d-axis current correction value i dc,ref The d-axis current command value i before addition d,ref is an example of the first current command value. The d-axis current correction value i dc,ref The d-axis current command value i d,refa is an example of a corrected current command value. dc The target voltage value v dc,ref The d-axis current correction value i dc,ref is the d-axis current command value i that determines the current output from the inverter 5. d,refSince the d-axis current correction value i dc,ref is the d-axis current command value i d,ref By directly adding this to the virtual synchronous generator control signal, the increase in the deviation between the DC power input to the inverter 5 and the AC power output from the inverter 5 is suppressed, so that the deviation of the DC voltage input to the inverter from its normal value can be suppressed, and virtual synchronous generator control can be continued stably.

[0115] 9 is a diagram showing a modified example of the functional blocks of the control device. The control device 20 may further include a power correction unit 33 and a subtractor 34 shown in FIG. 9 in addition to the functional blocks shown in FIG. 2. The power correction unit 33 corrects the output voltage measurement value v out The d-axis current correction value i dc,ref By multiplying this, the compensation power value P comp Calculate the output voltage measurement value v out is the measured value of the voltage actually output from the inverter 5 to the power grid 1. The output voltage measurement value v out is the measurement at node N between the filter 3 and the power system 1.

[0116] The frequency control unit 22 calculates the effective power measurement value P out Compensation power value P comp The voltage v output from the inverter circuit 8 is calculated by subtracting the value (active power correction measurement value) obtained by subtracting the active power v PWM By controlling the frequency of the inverter, the output voltage v output from the inverter 5 to the power grid 1 is out Frequency f out The d-axis current correction value i dc,ref is the d-axis current command value i d,ref When added to the measured active power value P out The output voltage v out Frequency f out A control error may occur in the control system that controls the active power measurement value P out Compensation power value P compBy subtracting, this control error can be suppressed so as to be cancelled out.

[0117] 10 is a functional block diagram showing an example of a power correction unit in the control device. The power correction unit 33 includes a dq conversion unit 33a, an amplitude calculation unit 33b, a multiplier 33c, and a multiplier 33d. The dq conversion unit 33a converts a phase command value θ ref Using this, the three-phase output voltage measurement value v out (Measured output voltages of phases A, B and C v out_a ,v out_b, v out_c ) to the output voltage measurement value v of the two axes out_d, v out_q The amplitude calculation unit 33b converts the d-axis output voltage measurement value v out_d and the measured output voltage on the q axis v out_q Using this, the output voltage measurement value v out The amplitude of |v out The multiplier 33c calculates the amplitude |v out | and d-axis current correction value i dc,ref The multiplier 33d multiplies the output value of the multiplier 33c by the amplitude adjustment coefficient K to obtain the compensation power value P comp The amplitude adjustment coefficient K is a coefficient for adjusting the units, and is basically 1 if the amount is handled in units.

[0118] 11 is a functional block diagram showing a first modified example of the DC voltage control unit. The DC voltage control unit 32A is a modified example of the above-mentioned DC voltage control unit 32. When the absolute value of the difference e is equal to or less than a predetermined value (for example, when the difference e is close to zero (|e|≦ε)), or when the value of the difference e is an intermediate value between a first predetermined value and a second predetermined value, the DC voltage control unit 32A calculates the d-axis current correction value i dc,ref The dead zone 32c is set so that the DC voltage measurement value v approaches zero (may include setting it to zero). ε represents a positive constant. dc and the target voltage value v dc,ref When the difference e between the d-axis current correction value i dc,refSince the addition of is suppressed, it is difficult to impede the operation of the pseudo-inertia control system in the control device 20, and it is possible to obtain a pseudo-inertia control inverter of the GFM control method that can operate more effectively.

[0119] 12 is a functional block diagram showing a second modified example of the DC voltage control unit. The DC voltage control unit 32B is a modified example of the DC voltage control unit 32. The DC voltage control unit 32B applies a high-pass filter 32d that attenuates signals having a frequency equal to or lower than a predetermined cutoff frequency to the difference e, and outputs a d-axis current correction value i dc,ref This calculates the DC voltage measurement value v dc and the target voltage value v dc,ref When the fluctuation of the difference e between the d-axis current and the dc,ref Therefore, the control system contributes only to DC voltage fluctuations caused by sudden fluctuations on the DC side, and contributes only to necessary phenomena, so that a pseudo-inertia controlled inverter of the GFM control method that can operate more effectively can be obtained. The high-pass filter 32d is an example of a high-pass filter.

[0120] The DC voltage control unit 32 may include both the dead zone 32c and the high-pass filter 32d.

[0121] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0122] 1 Power system 2. Power conversion device 3. Filters 4 Switch 5. Inverter 6 Power conversion section 7 Capacitor 8 Inverter Circuit 10 Power Lines 20 Control device 21 dq conversion section 22 Frequency Control Section 23 Voltage amplitude control section 25 Instantaneous current command section 27 Inverse dq transformation section 28 Instantaneous current control section 29 Adder 30 PWM pulse generator 31 Instantaneous voltage command unit 32 DC voltage control section 33 Power correction section 34 Subtractor 35 Adder

Claims

1. An inverter that converts input DC power into AC power; A control device that operates the inverter as a virtual synchronous generator, The control device includes: a power conversion device that controls the inverter using a corrected current command value obtained by adding a correction value that brings a DC voltage input to the inverter closer to a target voltage to a first current command value that contributes to an active power output from the inverter.

2. The control device includes: Calculating a compensation power value by multiplying a measurement value of an output voltage from the inverter by the correction value; 2. The power conversion device according to claim 1, wherein a frequency of the voltage output from the inverter is controlled using a value obtained by subtracting the compensation power value from the measured value of the active power.

3. 2. The power conversion device according to claim 1, wherein the control device applies a dead band in which the correction value is zero when an absolute value of a difference between the DC voltage and the target voltage is equal to or less than a predetermined value, or when the value of the difference is an intermediate value between a first predetermined value and a second predetermined value.

4. The power conversion device according to claim 1 , wherein the control device determines the correction value by applying a high-pass filter that attenuates signals having a frequency equal to or lower than a cutoff frequency to the difference between the DC voltage and the target voltage.

5. The control device includes:

5. The power conversion device according to claim 1, wherein a measured value of an output current from the inverter is converted into a d-axis current that contributes to the active power and a q-axis current that contributes to reactive power output from the inverter, and the d-axis current is set as the first current command value.

6. The control device includes: deriving a frequency command value for an output voltage from the inverter using the measured value of the active power and the measured value of a frequency of the output voltage from the inverter; deriving an amplitude command value for an output voltage of the inverter using the measured value of the reactive power; The power conversion device according to claim 5 , wherein a second current command value contributing to the reactive power is derived using the q-axis current, the frequency command value, and the amplitude command value.

7. The control device includes: The power conversion device according to claim 6 , wherein an output current command value that is a command value for an output current from the inverter is derived using the corrected current command value and the second current command value.

8. The control device includes: deriving an output voltage command value, which is a command value for the output voltage from the inverter, using the amplitude command value and a phase command value for the output voltage from the inverter; deriving an output voltage correction value that brings the output current of the inverter closer to the output current command value; The power conversion device according to claim 7 , wherein the inverter is controlled using a command value obtained by adding the output voltage correction value to the output voltage command value.

9. A control method for a power conversion device that operates an inverter that converts input DC power into AC power as a virtual synchronous generator, comprising: A control method for controlling the inverter using a corrected current command value obtained by adding a correction value that brings a DC voltage input to the inverter closer to a target voltage to a first current command value that contributes to an active power output from the inverter.

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