Power conversion device and power conversion system

Abstract

An electric power conversion device in an embodiment comprises: a harmonic filter for reducing an outflow of a harmonic current generated by an electric power converter; and a converter control unit for providing an operation command to the electric power converter. The converter control unit comprises an impedance compensation unit for outputting a compensation amount which compensates the voltage of an AC on the basis of an impedance compensation function adjusted such that the total impedance of the electric power converter and the harmonic filter in terms of of the AC becomes substantially infinite, a voltage / current control unit for controlling the voltage and / or the current of the electric power converter to achieve a target value on the basis of the compensation amount, and a gate signal generation unit for converting at least a voltage command value of the AC acquired from the voltage / current control unit to a gate signal to be provided to the electric power converter and outputting the gate signal. Accordingly, a negative resistance characteristic of the impedance of the electric power converter can be reduced, and an inflow of a harmonic current into the electric power converter is reduced, thereby achieving high stability over an entire frequency band.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to power conversion devices and power conversion systems. [Background technology]

[0002] In power converters connected to the grid, the interaction between grid impedance and converter control can generate harmonic resonance, leading to unstable operation and, in some cases, protective shutdown. In particular, in systems such as microgrids and offshore wind power generation systems where a large number of power converters are interconnected, there was a risk that their interactions could lead to serious resonance problems.

[0003] This situation is thought to be related to the negative resistance (which has a harmonic amplification effect) of the transducer impedance that appears due to factors such as delays in transducer control. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] X. Wang, MG Taul, H. Wu, Y. Liao, F. Blaabjerg and L. Harnefors: “Grid-Synchronization Stability of Converter-Based Resources-An Overview,” IEEE Open Jour. Ind. Appl. vol. 1, pp. 115-134 (2020-08) [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention has been made in view of the above, and aims to provide a power converter and a power converter system that reduce the negative resistance of the impedance of the power converter and suppress the inflow of harmonic current into the power converter, thereby achieving high stability over the entire frequency range. [Means for solving the problem]

[0006] The power converter of the embodiment is a power converter capable of converting AC to DC power, comprising: a power converter, a harmonic filter for reducing the outflow of harmonic currents generated by the power converter, and a converter control unit for giving operation commands to the power converter, wherein the converter control unit comprises: an impedance compensation unit that outputs a compensation amount for compensating the AC voltage based on an impedance compensation function adjusted so that the total impedance of the power converter and the harmonic filter as seen from the AC becomes substantially infinite; a voltage / current control unit that controls the voltage and / or current of the power converter to target values ​​based on the compensation amount; and a gate signal generation unit that converts at least the AC voltage command value obtained from the voltage / current control unit into a gate signal to be given to the power converter and outputs it. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic block diagram of the power conversion device according to the first embodiment. [Figure 2] Figure 2 is a block diagram illustrating the overall configuration of the AC information calculation unit. [Figure 3] Figure 3 is a schematic block diagram of the voltage and current control unit. [Figure 4] Figure 4 is a block diagram illustrating the schematic configuration of the impedance compensation unit. [Figure 5] Figure 5 is an explanatory diagram of an example of a transfer function model for a power converter. [Figure 6] Figure 6 is an explanatory diagram of the conventional problems. [Figure 7] Figure 7 is an explanatory diagram of the effects of the embodiment. [Figure 8] Figure 8 is an explanatory diagram illustrating a specific example of voltage and current control in a conventional converter control device. [Figure 9] FIG. 9 is an explanatory diagram of a specific example of voltage and current control in the converter control device of the embodiment. [Figure 10] FIG. 10 is a schematic configuration block diagram of the power conversion device according to the second embodiment. MODE FOR CARRYING OUT THE INVENTION

[0008] Next, the embodiments will be described in detail with reference to the drawings. [1] First Embodiment FIG. 1 is a schematic configuration block diagram of the power conversion device according to the first embodiment. The power conversion device 10 is provided at the system connection point P between the AC system and the DC system, and mutually converts the AC power supplied by the AC system ACP and the DC power supplied by the DC system DCP. In FIG. 1, the system impedance IM represents the impedance of the entire AC system ACP when viewed from the system connection point P side of the AC system ACP.

[0009] The AC system and the DC system may be a combination of a power source (for example, an AC power source ACP and a DC power source DCP) and a load (for example, a combination of a DC power source and an AC load) in addition to the case where both are power sources.

[0010] The power conversion device 10 includes a voltage sensor 11, a circuit breaker 12, a harmonic filter 13, a connection inductor 14, a current sensor 15, a converter control device 16, and a power converter 17. Here, the converter control device 16 functions as a converter control unit.

[0011] The voltage sensor 11 detects the AC voltage Vs at the system connection point P. The circuit breaker 12 connects or disconnects the power conversion device 10 to / from the AC power source ACP which is an external system. The harmonic filter 13 removes predetermined harmonic components. The harmonic filter 13 is designed to meet the harmonic standard of the system, and if the harmonic standard of the system is met, the harmonic filter 13 may not be provided.

[0012] The coupling inductor 14 is an equivalent coupling impedance that collectively represents the effective inductance with respect to the alternating current Isi (corresponding to the alternating currents Isr, Iss, and Ist of each phase) detected by the current sensor 15. The current sensor 15 detects the alternating current Is and outputs it to the converter control device 16.

[0013] The converter control device 16 includes an alternating current information calculation unit 21, a voltage / current control unit 22, a gate signal generation unit 23, and an impedance compensation unit 24.

[0014] Based on the alternating current voltage Vs at the system coupling point P, the alternating current information calculation unit 21 calculates the amplitude component and phase of the alternating current voltage Vs.

[0015] More specifically, the alternating current information calculation unit 21 performs a d-q rotating coordinate system conversion on the alternating current voltage Vs at the system coupling point P and outputs the alternating current system voltages Vsd and Vsq as the amplitude components of the alternating current voltage. Here, the alternating current system voltage Vsd is the alternating current system effective voltage, and the alternating current system voltage Vsq is the alternating current system reactive voltage.

[0016] Furthermore, the alternating current information calculation unit 21 repeatedly calculates to make the absolute value of one of the alternating current system voltages Vsd and Vsq zero, thereby calculating the alternating current frequency, and generates and outputs the alternating current system voltage phase theta by oscillating based on the calculated value of the alternating current frequency.

[0017] The voltage / current control unit 22 controls at least one of the voltage and current of the power converter 17 to a target value. The result of the control calculation is output as the voltage command value V * and output.

[0018] Also, the voltage / current control unit 22 performs feedback control on the alternating current based on the alternating current system voltage phase theta, which is the alternating current phase obtained from the alternating current information calculation unit 21, and the compensation alternating current voltage Vs' described later.

[0019] The gate signal generation unit 23 generates a voltage command value V, which includes at least an AC component, obtained by the voltage / current control unit 22. * This is converted to a gate signal (gate) and output to the power converter 17.

[0020] The impedance compensation unit 24 generates a compensated AC voltage Vs' (compensated AC voltages Vsr', Vss', Vst' for each phase) from the AC voltage Vs (corresponding to the AC voltages Vsr, Vss, Vst for each phase) in order to compensate for the characteristics of the converter impedance, taking into account the characteristics of the harmonic filter 13, and outputs it to the voltage / current control unit 22.

[0021] The power converter 17 is controlled based on the grid connection point voltage Vs obtained by the AC information calculation unit 21 and performs power conversion (AC power → DC power or DC power → AC power). It is also possible to configure the system to perform power conversion directly using fixed coordinate system calculation control without performing rotational coordinate transformation, that is, without using the information from the AC information calculation unit 21.

[0022] Here, we will explain the AC information calculation unit 21 in detail. Figure 2 is a block diagram illustrating the overall configuration of the AC information calculation unit. The AC information calculation unit 21 includes a conversion unit 31, a PI calculation unit 32, an adder unit 33, and an oscillator 34.

[0023] The conversion unit 31 acquires the R-phase voltage Vsr, S-phase voltage Vss, and T-phase voltage Vst corresponding to the AC voltage Vs of the grid connection point P detected by the voltage detector. The conversion unit 31 converts (calculates) the AC system voltage phase theta, which is the phase of the AC obtained from the AC information calculation unit 21, and the acquired R-phase voltage Vsr, S-phase voltage Vss, and T-phase voltage Vst into the AC system active voltage Vsd and the AC system reactive voltage Vsq using equation (1).

[0024]

number

[0025] The PI calculation unit 32 calculates the frequency difference (hereinafter referred to as frequency difference Δfpll) between the frequency of the AC system voltage to which the power converter 20 is connected and the reference AC system frequency fs0, based on the AC system reactive voltage Vsq converted by the conversion unit 31.

[0026] Here, the frequency difference Δfpll takes a positive value when the frequency of the AC system voltage is higher than the reference AC system frequency fs0, and a negative value when it is lower than the reference AC system frequency fs0. The reference AC system frequency fs0 is the rated frequency of the interconnected AC system (AC power supply ACP in Figure 1), and is, for example, 50 Hz or 60 Hz.

[0027] The frequency difference Δfpll continues to increase or decrease until the calculated value of the AC system reactive voltage Vsq input to the PI calculation unit 32 becomes zero, and converges to the difference between the actual AC system frequency and the reference AC system frequency fs0.

[0028] The summing unit 33 adds the frequency difference Δfpll calculated by the PI calculation unit 32 to the reference AC system frequency fs0. In the following description, the frequency obtained by adding the frequency difference Δfpll to the reference AC system frequency fs0 will be referred to as the AC frequency fpll.

[0029] The oscillator 34 outputs an AC system voltage phase theta that repeatedly increases monotonically from a minimum value of 0 to a maximum value of 2π, based on the frequency of the AC frequency fpll calculated by the summer 33.

[0030] As mentioned above, the AC system voltage phase theta is used for the conversion of the AC system active voltage Vsd and AC system reactive voltage Vsq of the conversion unit 31, and for AC current control.

[0031] In AC current control, when applying non-interference current control based on variables on a general rotating coordinate system, the AC system voltage phase theta is used for the rotational coordinate transformation, or inverse transformation (fixed coordinate transformation), of voltage and current values. Through the above-described process, the AC information calculation unit 21 obtains the AC system voltage phase theta by repeatedly calculating the AC system voltage phase theta so that the calculated value of the AC system reactive voltage Vsq in the conversion unit 31 becomes zero.

[0032] Next, the voltage / current control unit 22 will be described in detail. Figure 3 is a schematic block diagram of the voltage and current control unit. The voltage / current control unit 22 includes a 1 / Vs calculation unit 41, a 1 / Vs calculation unit 42, an ωs*Lvsc calculation unit 43, an ωs*Lvsc calculation unit 44, a calculation unit 45, a calculation unit 46, a PI calculation unit 47, a PI calculation unit 48, a calculation unit 49, a calculation unit 50, a rotation coordinate transformation unit 51, a fixed coordinate transformation unit 52, a calculation unit 53, a calculation unit 54, and a calculation unit 55.

[0033] The 1 / Vs calculation unit 41 calculates the active power command value p generated by, for example, an external device. * Perform the 1 / Vs operation on this. Here, Vs is the system voltage rating (constant). The 1 / Vs calculation unit 42 calculates the reactive power command value q generated, for example, by an external device. * A 1 / Vs calculation is performed on this value. Note that the outputs of the 1 / Vs calculation unit 41 and the 1 / Vs calculation unit 42 are values ​​based on the current.

[0034] The calculation unit 45 subtracts the active current Isd, which is the output of the rotation coordinate transformation unit 51, from the output of the 1 / Vs calculation unit 41. Furthermore, the calculation unit 46 subtracts the reactive current Isq, which is the output of the rotation coordinate transformation unit 51, from the output of the 1 / Vs calculation unit 42.

[0035] The PI calculation unit 47 performs proportional-integral calculation on the output of the calculation unit 45. The PI calculation unit 48 performs proportional-integral calculation on the output of the calculation unit 46.

[0036] The ωs*Lvsc calculation unit 43 multiplies the active current Isd, which is the output of the rotating coordinate conversion unit 51, by the system fundamental wave angular frequency ωs and the inductance value Lvsc of the coupling inductor, and outputs the result. Here, the system fundamental wave angular frequency ωs is a constant.

[0037] The ωs*Lvsc calculation unit 44 multiplies the reactive current Isq, which is the output of the rotating coordinate conversion unit 51, by the system fundamental wave angular frequency ωs and the inductance value Lvsc of the coupling inductor. In these cases, the outputs of the ωs*Lvsc calculation unit 43 and the ωs*Lvsc calculation unit 44 are values based on voltage.

[0038] The calculation unit 49 subtracts the output of the PI calculation unit 47 from the output of the ωs*Lvsc calculation unit 44. The calculation unit 50 reverses the sign of the sum of the output of the ωs*Lvsc calculation unit 43 and the output of the PI calculation unit 48.

[0039] The rotating coordinate conversion unit 51 converts the AC currents Isr, Iss, and Ist into AC current components Isd and Isq on the rotating coordinate axis synchronized with the detected phase theta detected from the voltage at the system connection point P.

[0040] The fixed coordinate conversion unit 52 converts the voltage amounts output by the calculation unit 49 and the calculation unit 50 into variables on the fixed coordinate axis, generates the primary voltage command value Vr1 * and outputs it to the calculation unit 53. Similarly, the fixed coordinate conversion unit 52 generates the primary voltage command value Vs1 * and outputs it to the calculation unit 54. Further, the fixed coordinate conversion unit 52 generates the primary voltage command value Vt1 * and outputs it to the calculation unit 55.

[0041] The calculation unit 53 adds the compensation AC voltage Vsr' that constitutes the compensation AC voltage Vs' of the impedance compensation unit 24 described later to the primary voltage command value Vr1 * and outputs the voltage command value Vr *

[0042] The calculation unit 54 uses the primary voltage command value Vs1 * ​The compensated AC voltage Vss' that constitutes the compensated AC voltage Vs' of the impedance compensation unit 24 described later is added to this to obtain the voltage command value Vs * Outputs.

[0043] The calculation unit 55 calculates the original voltage command value Vt1 * Adding the compensated AC voltage Vst' that constitutes the compensated AC voltage Vs' of the impedance compensation unit 24 described later, the voltage command value Vt * Outputs.

[0044] Next, the impedance compensation unit 24 will be described in detail. Figure 4 is a block diagram illustrating the schematic configuration of the impedance compensation unit. The impedance compensation unit 24 includes an impedance compensation function unit 61, a first compensation characteristic adjustment function unit 62, a second compensation characteristic adjustment function unit 63, and an adder unit 64.

[0045] Before providing a detailed explanation of the operation of the impedance compensation unit 24, the principle of this embodiment will be described. When the transducer impedance, including the harmonic filter 13, is ideally infinite, it becomes difficult for harmonic currents other than sine waves, which are adjusted by current control, to flow in.

[0046] Therefore, in this embodiment, we assume a certain compensation function and calculate inversely the characteristics that result in infinite transducer impedance.

[0047] Figure 5 is an explanatory diagram of an example of a transfer function model for a power converter. The transfer function models of power conversion devices are broadly composed of control models and circuit models.

[0048] The control model can be represented by the compensation characteristic Hff(s), the grid connection point voltage detection filter Fff(s), the grid connection point voltage detection delay Dff(s), the current control gain Gacr(s), the current control delay Dicalc(s), the PWM delay Dpwm(s), the AC current detection filter Ffb(s), and the AC current detection delay Dfb(s).

[0049] Furthermore, the circuit model can be represented using harmonic filters and interconnected inductors. In Figure 5, the magnitude of the AC current command value Isi*(s) is roughly proportional to the active power command value and the reactive power command value.

[0050] The alternating current Isi(s) is detected via the alternating current detection filter Ffb(s). The detection time includes the alternating current detection delay Dfb(s). The deviation of the alternating current Isi(s) from the alternating current command value Isi*(s) is then input to the current control gain Gacr(s). Here, the gain Gacr(s) is the gain for general proportional control or proportional-integral control.

[0051] The output of gain Gacr(s) is subtracted from the grid connection point voltage Vs(s) obtained via the compensation characteristic Hff(s), the grid connection point voltage detection filter Fff(s), and the grid connection point detection delay Dff(s).

[0052] The obtained subtraction result is output from the power converter as the converter AC terminal voltage V(s) via a current control delay Dicalc(s) and a PWM delay Dpwm(s).

[0053] The voltage difference between the grid connection point voltage Vs(s) and the converter AC terminal voltage V(s) is applied to the connection inductor (inductance Lsi, resistance Rsi), causing an AC current Isi(s) to flow. Furthermore, the grid connection point voltage Vs(s) is applied to the harmonic filter 13 (inductance Lf, capacitance Cf, resistance Rf), and a filter current If(s) flows through it.

[0054] The AC current Isi(s) and the filter current If(s) are added together to obtain the system current Is(s), which flows through the system impedance Zgrid(s). Subtracting the voltage drop Zgrid(s)Is(s) across the system impedance from the power supply voltage VG(s) yields the system connection point voltage Vs(s).

[0055] Here, we will explain the derivation of the impedance compensation function. Now, if the transducer impedance, including the harmonic filter, is ideally infinite, then harmonic currents other than the sinusoidal current controlled by current control will be less likely to flow in. Therefore, in this embodiment, we assume a certain impedance compensation function and calculate inversely the characteristic that makes the transducer impedance infinite.

[0056] In other words, assuming that the power grid connection point voltage detection value is compensated by the characteristic Hff(s), the converter impedance Zvsc(s) can be obtained from the transfer function model of the power converter shown in Figure 5, resulting in equation (2).

[0057]

number

[0058] However, Zfilter(s) is the impedance of the harmonic filter and can be expressed by equation (3).

[0059]

number

[0060] Conventionally, Hff(s)=1, but in this embodiment, Zvsc(s)→∞ We will calculate the Hff(s) that satisfies the given condition. In other words, by formulating an equation where "the denominator of the irreducible fraction of Zvsc(s) = 0" so that Zvsc(s) approaches infinity, and calculating the compensation characteristic Hff(s), we obtain equation (4).

[0061]

number

[0062] Furthermore, to simplify implementation into the control program, ignoring each delay time allows us to approximately obtain the compensation characteristic Hff(s) in equation (5).

[0063]

number

[0064] In this embodiment, the compensation characteristic Hff(s) is connected in series with the grid connection point voltage detection, but it can be connected at any position in the converter control. In this case, the converter impedance Zvsc(s) can be calculated by similarly assuming the connection point, and the characteristics of Hff(s) can be derived by working backward so that it becomes infinite. Furthermore, the compensation amount obtained from the compensation characteristics may be a voltage, current, or other physical quantity depending on the connection point. The compensated AC voltage Vs' is an example of a case where the compensation amount is a voltage. However, even if the compensation characteristic Hff(s) is connected at any point, the AC voltage output by the converter is ultimately and indirectly compensated.

[0065] Now, let's explain the problems with the conventional approach. Figure 6 is an explanatory diagram of the conventional problems. Figure 6(A) illustrates the relationship between the amplitude and frequency of the transducer impedance. Figure 6(B) illustrates the relationship between the phase and frequency of the transducer impedance.

[0066] In Figure 6, the transducer impedance Zvsc is the conventional characteristic, with Hff(s)=1 in equation (2). Conventionally, due to the effects of harmonic filters and control delay, negative resistance characteristics are observed in certain frequency ranges (the frequency range indicated by circle A in Figure 6(B)).

[0067] In this case, the negative resistance characteristic refers to the region where the phase of the transducer impedance Zvsc is greater than +90° and less than -90°, where the real part of the transducer impedance Zvsc is negative, and where harmonic resonances can be amplified. In other words, positive feedback occurs, such as a voltage drop due to the inflow of harmonic currents, and the harmonic currents increase.

[0068] In a typical resistor, the inflow of harmonic currents generates a counter-voltage, which suppresses the harmonic currents.

[0069] In contrast, the converter impedance Zvsc0 obtained in this embodiment is obtained by applying the compensation characteristic Hff(s) shown in equation (5), and the following characteristics are obtained. As shown in Figure 6(A), the amplitude of the transducer impedance in the low-frequency range increases, making it more difficult for harmonic currents to flow in the low-frequency range.

[0070] Furthermore, in the conventional transducer impedance Zvsc, the phase of the transducer impedance in the frequency range (indicated by circle A in Figure 6(B)), which previously exhibited negative resistance characteristics, is now within ±90 degrees, thus eliminating the negative resistance characteristic.

[0071] Furthermore, in relation to the system impedance, if the resonant frequency falls within the frequency range where conventional negative resistance characteristics were observed (the frequency range indicated by circle A in Figure 6(B)), harmonic resonance is suppressed. This is because the negative resistance characteristics caused by the harmonic filter were reduced by approximately compensating for the transducer impedance to become infinite when integrated with the harmonic filter.

[0072] On the other hand, as shown in Figure 6(B), negative resistance characteristics appear in the low-frequency and high-frequency ranges (frequency ranges indicated by circle B in Figure 6(B)), and in relation to the system impedance, harmonic resonance occurs when the resonant frequency falls within these frequency ranges.

[0073] As explained above, the impedance compensation function Hff(s) in equation (5) can suppress harmonic resonances in the conventional resonant frequency range, but it can potentially generate new harmonic resonances in the surrounding frequency range.

[0074] Therefore, in this embodiment, the impedance compensation function Hff(s) is adjusted to act only in the frequency range near FB, which conventionally exhibited negative resistance characteristics.

[0075] More specifically, for example, let the impedance compensation function Hff(s) be the adjusted compensation function Hff'(s) in equation (6).

[0076]

number

[0077] Here, Fbpf(s) is a band-pass filter with a center frequency f0 (where f0 is assumed to be within the frequency range FB in Figure 6(B)). By using the impedance compensation function as shown in equation (6), the characteristics of the impedance compensation function Hff(s) can be made to act only near the center frequency f0, thereby reducing the influence on the surrounding frequency range (generation of harmonic resonance).

[0078] In this embodiment, we have described the case where adjustment is performed by combining a band-pass filter, but to obtain a similar effect, it is also possible to configure it in combination with a low-pass filter, a high-pass filter, a band-reject filter, etc., and adjust it so that the impedance compensation function Hff(s) acts only near the center frequency f0.

[0079] In equation (6), "Hff(s)" is an example of the impedance compensation function shown in Figure 4, "Fbpf(s)" is an example of the first compensation characteristic adjustment function, and "1" is an example of the second compensation characteristic adjustment function. In other words, the impedance compensation function is an approximation function that makes the transducer impedance virtually infinite, and the compensation characteristic adjustment function is realized by a digital filter or the like to limit the effect of the impedance compensation function to a certain effective frequency range.

[0080] Furthermore, the first compensation characteristic adjustment function is calculated in series with the impedance compensation function, allowing signals in the effective frequency range to pass through. The second compensation characteristic adjustment function is calculated in parallel with the impedance compensation function, allowing signals in the frequency range at least lower than the effective frequency range to pass through.

[0081] If Fff(s), which is calculated in series with the impedance compensation function Hff'(s), is a low-pass filter commonly used for noise reduction, then the output will be a sum of a signal that includes frequencies lower than the effective frequency range and a signal with the impedance compensation function applied to the effective frequency range.

[0082] Here, in order to eliminate the effects of the detection delay time, detection error, and delay time required for rotational coordinate transformation calculations of the system voltage detection phase theta, and to achieve stable control, it is desirable to calculate the impedance compensation function on a fixed coordinate system (without performing rotational coordinate transformation using theta).

[0083] Figure 7 is an explanatory diagram of the effects of the embodiment. Figure 7(A) illustrates the relationship between the amplitude and frequency of the transducer impedance. Figure 7(B) illustrates the relationship between the phase and frequency of the transducer impedance.

[0084] In Figure 7, Zvsc1 is obtained by applying the adjusted impedance compensation function H'ff(s) from equation (6), and has the following characteristics. According to the adjusted impedance compensation function H'ff(s), negative resistance characteristics are reduced across the entire frequency range, and harmonic resonances can be suppressed under many system conditions.

[0085] Furthermore, according to the adjusted impedance compensation function H'ff(s), as shown by the solid line in Figure 7(B), the impedance amplitude in the low-frequency range is maintained at the same level as before, and the harmonic currents in the low-frequency range are suppressed to a level comparable to before. In addition, the control response (generally proportional to the impedance amplitude) is also maintained at a level comparable to before.

[0086] Next, the effects of the embodiment will be described in more detail. Figure 8 is an explanatory diagram illustrating a specific example of voltage and current control in a conventional converter control device. Figure 8(A) is an explanatory diagram of the AC voltage waveform in a conventional converter control device. Figure 8(B) is an explanatory diagram of the AC current waveform in a conventional converter control device.

[0087] As shown in Figure 8(A), the AC voltage waveform is unstable in amplitude due to the influence of harmonic resonance. As shown in Figure 8(B), the AC current waveform also shows unstable amplitude due to the influence of harmonic resonance.

[0088] Figure 9 is an explanatory diagram illustrating a specific example of voltage and current control in the converter control device of the embodiment. Figure 9(A) is an explanatory diagram of the AC voltage waveform in the converter control device of the embodiment. Figure 9(B) is an explanatory diagram of the AC current waveform in the converter control device of the embodiment.

[0089] As shown in Figure 9(A), the AC voltage waveform of the embodiment has a much more stable amplitude compared to the conventional AC voltage waveform in Figure 8(A), due to the suppression of harmonic resonance.

[0090] As shown in Figure 9(B), the AC current waveform of the embodiment also exhibits significantly more stable amplitude compared to the conventional AC current waveform in Figure 8(B), due to the suppression of harmonic resonance.

[0091] As described above, according to this first embodiment, the negative resistance of the impedance of the power converter is reduced, and the inflow of harmonic current into the power converter is suppressed, resulting in high stability across the entire frequency range.

[0092] [2] Second embodiment Figure 10 is a schematic block diagram of the power conversion device according to the second embodiment. In Figure 10, the same reference numerals are used for parts that are the same as those in the first embodiment of Figure 1.

[0093] The difference between this second embodiment and the first embodiment is that it includes a resonance state detection unit 71 that detects a resonance state based on AC system voltages Vsd and Vsq, and is configured to continue impedance compensation only if a predetermined resonance state is not detected by the resonance state detection unit during impedance compensation, and to disable impedance compensation if a predetermined resonance state is detected during impedance compensation.

[0094] In this case, a predetermined resonance state is detected when, in a state where impedance compensation is being performed by the impedance compensation unit 24A, harmonics above a predetermined harmonic level are detected, and the accuracy of the compensation by the impedance compensation unit 24A is impaired, potentially increasing harmonic resonance amplification as a result of the compensation.

[0095] The power converter 10 includes a voltage sensor 11, a circuit breaker 12, a harmonic filter 13, a grid-connecting inductor 14, a current sensor 15, a converter control device 16A, and a power converter 17.

[0096] The converter control device 16 of the power converter 10 in the second embodiment includes an AC information calculation unit 21, a voltage / current control unit 22, a gate signal generation unit 23, an impedance compensation unit 24A, and a resonance state detection unit 71.

[0097] The AC information calculation unit 21 calculates the amplitude component and phase of the AC voltage Vs based on the AC voltage Vs at the grid connection point P. More specifically, the AC information calculation unit 21 performs a dq rotation coordinate system transformation on the AC voltage Vs at the grid connection point P, and outputs the AC system voltages Vsd and Vsq as amplitude components of the AC voltage. Here, the AC system voltage Vsd is the AC system active voltage, and the AC system voltage Vsq is the AC system reactive voltage.

[0098] Furthermore, the AC information calculation unit 21 calculates the AC frequency by repeatedly performing calculations so that the absolute value of one of the AC system voltages Vsd or Vsq becomes zero, and generates and outputs the AC system voltage phase theta by oscillating based on the calculated value of the AC frequency.

[0099] The voltage / current control unit 22 controls at least one of the voltage and current of the power converter 17 to a target value. The result of the control calculation is the voltage command value V * Output as follows.

[0100] Furthermore, the voltage / current control unit 22 provides feedback control of the AC current based on the AC system voltage phase theta, which is the phase of the AC obtained from the AC information calculation unit 21, and the compensated AC voltage Vs', which will be described later.

[0101] The gate signal generation unit 23 generates a voltage command value V, which includes at least an AC component, obtained by the voltage / current control unit 22. * This is converted to a gate signal (gate) and output to the power converter 17.

[0102] When the impedance compensation unit 24A receives a control signal ctrl corresponding to the case where a predetermined resonance state is not detected by the resonance state detection unit 71 (described later), it generates a compensated AC voltage Vs' (compensated AC voltages Vsr', Vss', Vst' for each phase) from the AC voltage Vs (corresponding to the AC voltages Vsr, Vss, Vst for each phase) in order to compensate the characteristics of the converter impedance using characteristics that take into account the harmonic filter 13, and outputs it to the voltage / current control unit 22.

[0103] Furthermore, when the impedance compensation unit 24A receives a control signal ctrl corresponding to the detection of a predetermined resonance state by the resonance state detection unit 71 (described later), it passes the AC voltage Vs (corresponding to the AC voltages Vsr, Vss, and Vst of each phase) as is, and outputs the AC voltages Vsr, Vss, and Vst of each phase as a compensated AC voltage Vs' to the voltage / current control unit 22, effectively not performing compensation.

[0104] The power converter 17 is controlled based on the grid connection point voltage Vs obtained by the AC information calculation unit 21 and performs power conversion (AC power → DC power or DC power → AC power). It is also possible to perform power conversion directly using fixed coordinate system calculation control without performing rotational coordinate transformation, that is, without using the information from the AC information calculation unit 21.

[0105] Here, the resonance state detection unit 71 will be described in detail. In its initial state, the resonance state detection unit 71 enables the processing of the impedance compensation unit 24A, that is, it enables a state in which a predetermined resonance state has not been detected.

[0106] Subsequently, the resonance state detection unit 71 detects harmonic components using Fourier transform or the like, and when the detected harmonic level becomes high, it outputs a control signal ctrl that disables the processing of the impedance compensation unit 24A, thereby disabling the calculations of the impedance compensation unit 24A. That is, the compensation characteristic Hff(s) = 1.

[0107] More specifically, for example, when constants (such as capacitance Cf) change due to the degradation of the harmonic filter, and the accuracy of compensation due to the compensation characteristic Hff(s)≠1 is impaired and instability occurs, disabling impedance compensation can prevent further harmonic resonance amplification.

[0108] Furthermore, it is possible to normally disable the processing of the impedance compensation unit 24A, and then control the system so that the processing of the impedance compensation unit 24A is enabled only when the harmonic level is higher than a predetermined harmonic level (a predetermined threshold) using the resonance state detection unit 71. In addition, the object to be detected for detecting the harmonic level may be either AC voltage or AC current.

[0109] As described above, according to this second embodiment, similar to the first embodiment, the negative resistance of the impedance of the power converter is reduced, and the inflow of harmonic current into the power converter is suppressed, resulting in high stability across the entire frequency range.

[0110] Furthermore, according to this second embodiment, by performing processing in the impedance compensation section, it is possible to suppress the increase in the negative resistance of the impedance of the power converter and the increase in the inflow of harmonic current into the power converter, thereby enabling more favorable impedance compensation.

[0111] [3] Modified examples of embodiments The converter control device or control device of this embodiment includes a control device such as a CPU, a storage device such as ROM (Read Only Memory) or RAM, an external storage device such as an HDD, a display device such as a liquid crystal display device for displaying various input / output interfaces and information, and an input device such as operation buttons, and has a hardware configuration that uses a normal computer.

[0112] The converter control device or the program executed by the control device of this embodiment is provided as an installable or executable file, recorded on a computer-readable recording medium such as a USB memory stick, an SSD (Solid State Drive), or a DVD (Digital Versatile Disk).

[0113] Furthermore, the converter control device or the program executed by the control device of this embodiment may be configured to be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. Alternatively, the converter control device or the program executed by the control device of this embodiment may be provided or distributed via a network such as the Internet.

[0114] Furthermore, the converter control device or the program for the control device of this embodiment may be provided pre-installed in a ROM or the like.

[0115] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0116] 10 Power converter 11 Voltage Sensor 12 Circuit breakers 13. Harmonic Filters 14 interconnected inductors 15 Current Sensor 16 Converter control unit 16A Converter Control Unit 17 Power Converters 20 Power Converters 21 Exchange information calculation section 22 Voltage / Current Control Unit 23 Gate signal generation unit 24, 24A Impedance Compensation Section 31 Conversion section 32 PI calculation section 33 Addition section 34 Oscillators 41, 42 1 / Vs calculation section 43, 44 ωs*Lvsc calculation section 45, 46 Arithmetic section 47, 48 PI calculation section 49, 50 Arithmetic section 51 Rotational Coordinate Transformation Unit 52 Fixed Coordinate Transformation Unit 53, 54, 55 Arithmetic section 61 Impedance Compensation Function Section 62 First Compensation Characteristic Adjustment Function Section 63 Second Compensation Characteristic Adjustment Function Section 64 Addition section 71 Resonance state detection unit ACP AC system Cf capacitance DCP DC system IM system impedance If filter current Is grid current Is alternating current Isd AC current component ISD (Active Current) Isi AC current command value Isi alternating current Isi ·Alternating current Isq (Reactive Current) Isr alternating current Lf Inductance LSI Inductance Lvsc Inductance Value P System Interconnection Point Rf resistance Rsi resistance V(s) Converter AC Terminal Voltage V * Voltage command value VG Power supply voltage Vs AC voltage Vs' Compensated AC Voltage

Claims

1. A power converter having a power converter, capable of converting AC and DC power, A harmonic filter that reduces the outflow of harmonic currents generated by the power converter, The system comprises a converter control unit that provides operation commands to the power converter, The converter control unit, An impedance compensation unit outputs a compensation amount to compensate for the AC voltage based on an impedance compensation function adjusted so that the total impedance of the power converter and the harmonic filter as seen from the AC becomes substantially infinite. A voltage / current control unit controls the voltage and / or current of the power converter to target values ​​based on the compensation amount, A gate signal generation unit that converts at least the AC voltage command value obtained from the voltage / current control unit into a gate signal to be given to the power converter and outputs it, A power conversion device equipped with this device.

2. The impedance compensation unit uses a function as the impedance compensation function such that the denominator of the irreducible fraction of the transfer function of the total impedance is approximately zero. The power conversion device according to claim 1.

3. The impedance compensation unit calculates the compensation amount using the AC voltage as an input parameter based on the impedance compensation function. The power conversion device according to claim 1.

4. The impedance compensation unit includes a first compensation characteristic adjustment function unit that selectively applies the impedance compensation function to a predetermined part of the effective frequency range when calculating the compensation amount. The power conversion device according to claim 1.

5. The first compensation characteristic adjustment function unit applies a first compensation characteristic adjustment function that selectively passes only a portion of the effective frequency range from the original compensation amount, which is the calculation result of the impedance compensation function, and outputs it as the first original compensation amount. The impedance compensation unit further includes a second compensation characteristic adjustment function unit that applies a second compensation characteristic adjustment function to the input AC voltage, which allows components in a frequency range lower than the effective frequency range to pass through, and outputs it as a second original compensation amount. An adder that adds the first original compensation amount and the second original compensation amount and outputs the compensation amount, The power conversion device according to claim 4, comprising:

6. The effective frequency range includes a frequency range in which the real part of the total impedance is a negative value. The power conversion device according to claim 4.

7. The system includes a resonance state detection unit that detects a resonance state based on harmonic components contained in the voltage and / or current at the grid connection point, and outputs a control signal to enable or disable the processing of the impedance compensation unit based on the resonance state. The impedance compensation unit outputs the compensation amount based on the control signal if the processing of the impedance compensation unit is effective, and outputs the input of the impedance compensation unit as is if the processing of the impedance compensation unit is ineffective. The power conversion device according to claim 1.

8. The processing of the impedance compensation unit is performed based on a quantity of voltage or current on a fixed coordinate axis. The power conversion device according to claim 1.

9. A power conversion system comprising a power converter capable of converting AC and DC power, a harmonic filter for reducing the outflow of harmonic currents generated by the power converter, a converter control unit for giving operation commands to the power converter, and a control device for controlling the power converter, The aforementioned power converter is An impedance compensation unit outputs a compensation amount to compensate for the AC voltage based on an impedance compensation function adjusted so that the total impedance of the power converter and the harmonic filter as seen from the AC becomes substantially infinite. A voltage / current control unit controls the voltage and / or current of the power converter to target values ​​based on the compensation amount, The system includes a gate signal generation unit that converts at least the AC voltage command value obtained from the voltage / current control unit into a gate signal to be given to the power converter and outputs it, Power conversion system.

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