Power conversion system and compensation control device

Abstract

To ensure stability in an easy manner even when a system impedance condition is changed as a result of a system-side configuration change or the like.SOLUTION: A power conversion system according to an embodiment is capable of converting DC power to AC power and AC power to DC power. A power conversion device includes: a power converter including a switching element capable of adjusting the voltage of AC power or the current of AC power; and a converter control unit including an interface unit, a voltage / current control unit that generates and outputs a voltage command value for controlling the voltage of AC power or the current of AC power, and a gate command generation unit that generates a gate signal to be given to the switching element on the basis of the voltage command value, so as to give an operation command to the switching element. A compensation control device is attachable to / detachable from the power conversion device via the interface unit, and compensates a feedback signal on the voltage of AC power and / or the current of AC power to the voltage / current control unit, and outputs the compensation feedback signal to the converter control unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a power conversion system and a compensation control device. [Background technology]

[0002] In power converters connected to the grid, voltage resonance can occur due to the interaction between the grid impedance (caused by grid wiring and loads) and the converter control, potentially leading to unstable operation and the inability to continue operation. Since the resonance pattern depends on unknown grid impedance conditions that change constantly from location to location and time to time, the resonance frequency may fluctuate due to changes in grid conditions. Therefore, even when stable control parameters are applied under specific conditions, changes in grid conditions may destabilize grid-connected operation.

[0003] A method has been proposed that estimates the system impedance and reduces the control sensitivity in the vibration frequency band using a notch filter or the like set based on the estimation results. However, with such a method, simply reducing the control sensitivity is not enough to ensure sufficient stability margin, and resonance may be amplified by even slight disturbances. Furthermore, such methods do not take into account cases where the system conditions (system impedance) are severe for stable operation. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-106843 [Non-patent literature]

[0005] [Non-Patent Document 1] H. Saad, Y. Fillion, S. Deschanvres, Y. Vernay and S. Denneti ere: ”On Resonances and Harmonics in HVDC-MMC Station Connected to AC Grid” IEEE Trans. Pow. Del., vol. 32, no. 3, pp. 1565-1573 (2017-06) [Overview of the project] [Problems that the invention aims to solve]

[0006] However, with conventional technology, when a power converter was constructed to match a predetermined grid condition, if the grid configuration changed or the grid impedance conditions changed, it was necessary to fundamentally change the configuration of the power converter, which could not be easily addressed.

[0007] The present invention has been made in view of the above, and aims to provide a highly reliable power conversion system that can easily ensure stability even when the grid impedance conditions change due to changes in the grid configuration or the like. [Means for solving the problem]

[0008] The power conversion system of the embodiment includes a power conversion device and a compensation control device, and is a power conversion system capable of mutually converting DC power and AC power. The power conversion device includes a power converter including a switching element capable of adjusting the voltage or current of AC power, an interface unit, a voltage / current control unit that generates and outputs a voltage command value for controlling the voltage or current of AC power, and a gate command generation unit that generates a gate signal applied to the switching element based on the voltage command value, and includes a converter control unit that gives an operation command to the switching element. The compensation control device is detachable from the power conversion device via the interface unit, and compensates the feedback signal to the voltage / current control unit of the voltage and / or current of AC power and outputs it to the converter control unit as a compensation feedback signal. Furthermore, the converter control unit can select the signal used to calculate the voltage command value in the voltage / current control unit from a feedback signal based on the voltage or current of the AC power, and a compensation feedback signal output by the compensation control unit.

Brief Description of Drawings

[0009] [Figure 1] FIG. 1 is a schematic configuration block diagram of the power conversion system according to the first embodiment. [Figure 2] FIG. 2 is a schematic configuration block diagram of the compensation calculation function unit. [Figure 3] FIG. 3 is an equivalent circuit diagram showing an example of the power conversion device and system impedance according to the present embodiment. [Figure 4] FIG. 4 is an explanatory diagram of a power conversion example in the R phase of the power converter in the first configuration example. [Figure 5] FIG. 5 is an explanatory diagram of a power conversion example in the R phase of the power converter in the second configuration example. [Figure 6] FIG. 6 is a schematic configuration block diagram of the power conversion system according to the second embodiment. [Figure 7] FIG. 7 is a schematic configuration block diagram of the power conversion system according to the third embodiment. [Figure 8] FIG. 8 is a schematic configuration block diagram of the power conversion system according to the fourth embodiment. [Figure 9] FIG. 9 is a schematic configuration block diagram of the compensation calculation function unit. [Figure 10]FIG. 10 is a diagram showing an example of impedance characteristics of the power conversion device according to the fourth embodiment. [Figure 11] FIG. 11 is a diagram showing an example of a vector diagram of the impedance of the power conversion device according to the fourth embodiment.

Embodiments for Carrying Out the Invention

[0010] [1] First Embodiment FIG. 1 is a schematic configuration block diagram of the power conversion system according to the first embodiment. The power conversion system 10 includes a power conversion device 11 that mutually converts a DC power supply and an AC power supply to perform system connection with the AC commercial system ACG, and a compensation control device 12 that is detachably connected to the power conversion device 11 and suppresses an increase in a predetermined harmonic component included in the AC voltage or AC current output by the power conversion device 11.

[0011] In this case, the power conversion device 11 can perform power conversion and system connection even when the compensation control device 12 is not mounted. In other words, by mounting the compensation control device 12, even when the system impedance condition changes due to a change in the system-side configuration while the configuration of the power conversion device 11 remains the same, it is possible to easily cope with the change, and thus it is possible to easily provide a highly reliable power conversion system with ensured stability.

[0012] The AC commercial system ACG includes an AC power supply PSAC and a system impedance ACIM that represents the impedance of the entire AC commercial system ACG.

[0013] The power conversion device 11 includes a power converter 21, a current detection sensor (CT) 22, a connection inductor 23, a voltage detection sensor (VT) 24, and a converter control unit 25. <00001{12}>The power converter 21 has multiple switching elements and can perform DC / AC conversion to mutually convert between three-phase AC power and DC power. The power converter 21 is connected to the AC commercial power grid via the interconnection inductor 23.

[0014] The current detection sensor 22 detects the AC currents Isr, Iss, and Ist of each phase flowing into the power converter 21 and outputs them as AC current detection signals to the converter control unit 25. The interconnection inductor 23 functions as a harmonic filter to prevent harmonic components from flowing from the power converter 21 into the grid. Although not shown in the diagram, a harmonic filter may also be configured by connecting additional passive elements such as capacitors.

[0015] The voltage detection sensor 24 detects the AC voltage of each phase of the AC power at the grid connection point GIP and outputs it to the converter control unit 25 as an AC voltage detection signal (=Vsr, Vss, Vst). The converter control unit 25 controls the power converter 21 using a gate control signal gate.

[0016] Next, the compensation control device 12 will be described. The compensation control device 12 includes an AD conversion unit 31, a compensation calculation function unit 32, and a DA conversion unit 33. The AD conversion unit 31 performs analog-to-digital conversion of the AC current detection signals (=Isr, Iss, Ist) input from the current detection sensor 22 and the AC voltage detection signals (=Vsr, Vss, Vst) input from the voltage detection sensor 24, and outputs them to the compensation calculation function unit 32.

[0017] The compensation calculation function unit 32 performs compensation calculations on the AC current detection signals (=Isr, Iss, Ist) and AC voltage detection signals (=Vsr, Vss, Vst) and outputs the compensation calculation results to the DA conversion unit 33.

[0018] The DA conversion unit 33 performs a digital-to-analog conversion of the compensation calculation result from the input compensation calculation function unit 32 and outputs it to the converter control unit 25 as compensated AC current detection signals CIsr, CIss, CIst and compensated AC voltage detection signals CVsr, CVss, CVst.

[0019] Here, we will describe the detailed configuration of the compensation calculation function unit 32. Figure 2 is a block diagram illustrating the overview configuration of the compensation calculation function unit. The compensation calculation function unit 32 includes a resonance state detection unit 32A and a sensitivity reduction unit 32B.

[0020] The resonance state detection unit 32A detects the vibration period (reciprocal of frequency) using a Fourier transform or counter on the detected values ​​of the AC voltages Vsr, Vss, and Vst, and extracts a vibration frequency fres or a vibration frequency band containing the vibration frequency fres, which is a state in which the harmonic amplitude exceeds a predetermined threshold within a predetermined frequency range.

[0021] In this case, the predetermined frequency range is set in advance to, for example, the range in which vibration frequency components are to be suppressed by the sensitivity reduction unit 32B. Alternatively, the predetermined frequency range may be set as, for example, a harmonic regulation range defined by some standard or a range in which a high risk of resonance occurrence has been identified through prior analysis.

[0022] Here, when the resonance state detection unit 32A detects a resonance state, it activates sensitivity reduction in the sensitivity reduction unit 32B, thereby reducing its sensitivity to the voltage / current control unit 43. The resonance state detection unit 32A detects the harmonic components of AC voltages Vsr, Vss, Vst or AC currents Isr, Iss, Ist. In this application, "A or B" is not limited to either A or B, but includes both A and B.

[0023] The resonance state detection unit 32A detects AC voltages Vsr, Vss, Vst or AC currents Isr, Iss, Ist, and detects vibration frequencies or vibration frequency bands within a predetermined frequency range where the harmonic amplitude exceeds a predetermined threshold. In the example in Figure 2, the resonance state detection unit 32A detects vibration frequencies or vibration frequency bands where the harmonic amplitude is greater than or equal to a predetermined threshold, based on the AC voltages Vsr, Vss, Vst. For example, the resonance state detection unit 32A identifies the frequency component with a large harmonic amplitude as the vibration frequency by performing a Fourier transform operation. Alternatively, the resonance state detection unit 32A may observe the vibration period of the AC voltages Vsr, Vss, Vst or AC currents Isr, Iss, Ist, and identify the vibration frequency by, for example, calculating the reciprocal of the vibration period.

[0024] The sensitivity reduction unit 32B reduces the sensitivity of the control in a frequency band that includes at least the vibration frequency. The sensitivity reduction unit 32B outputs AC currents with reduced sensitivity to AC currents Isr, Iss, and Ist, and AC voltages with reduced sensitivity to AC voltages Vsr, Vss, and Vst, in a state of reduced sensitivity to the voltage / current control unit 43.

[0025] More specifically, the sensitivity reduction unit 32B performs, for example, digital filtering on the AC voltages Vsr, Vss, Vst and AC currents Isr, Iss, Ist to attenuate components in the vibration frequency band fres. Here, the digital filter may be a low-pass filter having a cutoff frequency lower than the vibration frequency, a notch filter that attenuates the band including the vibration frequency, or a combination thereof.

[0026] Furthermore, when a low-pass filter and a notch filter are combined, the attenuation rate in the vibration frequency band (fres) can be increased compared to when they are not combined. Some or all of the characteristics of the digital filter are dynamically adjusted to effectively attenuate the vibration frequency band (fres) extracted by the resonance state detection unit 32A.

[0027] In this case, the cutoff frequency of the low-pass filter may be fixed to a value at least higher than the fundamental frequency. Furthermore, the sensitivity reduction unit 32B may dynamically change its sensitivity reduction characteristics with respect to the voltage / current control unit 43 according to the vibration frequency fres. By reducing the sensitivity of the voltage / current control unit 43 in the vibration frequency fres band, amplification of the voltage / current components at vibration frequency fres can be prevented. In other words, the sensitivity reduction unit has the effect of improving the stability of the converter control to at least a stable limit that does not lead to divergence.

[0028] Next, an example of a power converter 11 and grid impedance will be described. Figure 3 is an equivalent circuit diagram showing an example of a power conversion device and grid impedance according to this embodiment. As shown in Figure 3, the AC system consists of the equivalent inductance Lgrid from the AC power source to the grid connection point and the equivalent capacitance Cgrid at the grid connection point. In the following explanation, the impedance seen from the grid connection point towards the AC power source is referred to as the system impedance Zgrid. The power converter 21 is connected to the grid connection point GIP via the connection inductor Lvsc.

[0029] Next, the detailed configuration of the converter control unit 25 will be described. As shown in Figure 1, the converter control unit 25 includes an interface (IF) unit 41, an AD conversion unit 42, a voltage / current control unit 43, and a gate command generation unit 44. When the compensation control device 12 is not connected, the interface unit 41 outputs the AC current detection signals (=Isr, Iss, Ist) input from the current detection sensor 22 and the AC voltage detection signals (=Vsr, Vss, Vst) input from the voltage detection sensor 24 to the AD conversion unit 42.

[0030] Furthermore, when the compensation control device 12 is connected, the interface unit 41 outputs the compensated AC current detection signals CIsr, CIss, CIst and the compensated AC voltage detection signals CVsr, CVss, CVst, which are the compensation calculation results of the compensation calculation function unit 32, to the AD conversion unit 42 instead of the AC current detection signals (=Isr, Iss, Ist) input from the current detection sensor 22 and the AC voltage detection signals (=Vsr, Vss, Vs) input from the voltage detection sensor 24.

[0031] The AD conversion unit 42 performs analog-to-digital conversion of AC current detection signals (=Isr, Iss, Ist) and AC voltage detection signals (=Vsr, Vss, Vs), or compensated AC current detection signals CIsr, CIss, CIst and compensated AC voltage detection signals CVsr, CVss, CVst, and outputs them to the voltage / current control unit 43.

[0032] The voltage / current control unit 43 determines the voltage command value Vr based on the AC current detection signal (=Isr, Iss, Ist) and the AC voltage detection signal (=Vsr, Vss, Vs), or the digital data corresponding to the compensated AC current detection signals CIsr, CIss, CIst and the compensated AC voltage detection signals CVsr, CVss, CVst. * Vs * , Vt * It generates and outputs to the gate command generation unit 44.

[0033] The gate command generation unit 44 generates a voltage command value Vr * Vs * , Vt * Based on this, a gate control signal gate is generated and output to the power converter 21.

[0034] Here, we will describe a first configuration example of the power converter 21. The power converter 21 employs, for example, a two-level converter and triangular wave comparative modulation. Figure 4 is an explanatory diagram of a power conversion example in the R phase of the power converter in the first configuration example. As shown in the upper part of Figure 4, the power converter 21 uses a triangular wave TR as the carrier signal and a voltage command value Vr *Compare it with the voltage command value Vr * When it is during the period when the voltage command value Vr is greater than or equal to the triangular wave TR, as shown in the middle row of FIG. 4, the gate control signal gate_rp corresponding to the R phase corresponding to the gate control signal gate is set to "1". When the voltage command value Vr * is less than the triangular wave TR, the gate control signal gate_rp corresponding to the R phase is set to "0".

[0035] As a result, as shown by the solid line in the lower row of FIG. 4, the alternating current Isr corresponding to the R phase gradually increases during the period when the gate control signal gate_rp is "0", and gradually decreases during the period when the gate control signal gate_rp is "1", and changes according to the voltage command value Vr * and is controlled to an alternating current as shown by the dashed line on average. By performing sampling processing at the black circles (the peaks and valleys of the triangular wave TR) in the lower row of FIG. 4, an average alternating current excluding the switching ripple can be detected. As a result, it is possible to prevent the operation of the converter from being destabilized by amplifying the switching ripple through control calculation. However, the triangular wave TR is generated by the gate command generation unit 44 of the subsequent converter control unit 25, and if it is the same as the prior art, the timing of the sampling process will easily deviate from the peaks and valleys of the triangular wave. If the timing of the sampling process deviates, an incorrect average alternating current will be detected, and for example, the operation of the converter will be destabilized by amplifying the switching ripple through control calculation. [[ID=!12]]

[0036] Therefore, in order to solve the problem of the first configuration example, a second configuration example of the power converter 21 will be described. In the second configuration example, the power converter 21 also adopts a two-level converter and triangular wave comparison modulation, similar to the first configuration example.

[0037] FIG. 5 is an explanatory diagram of a power conversion example in the R phase of the power converter in the second configuration example. The difference between this second configuration example and the first configuration example is that the compensation control device 12 performs sampling processing at a frequency higher than twice the frequency of the triangular wave TR as the carrier signal.

[0038] As shown in the upper part of Figure 5, the power converter 21 uses a triangular wave TR as the carrier signal and a voltage command value Vr * Compare this with the voltage command value Vr * During the period when the voltage is greater than or equal to a triangular wave TR, as shown in the middle of Figure 5, the gate control signal gate_rp corresponding to the R phase is set to "1", and the voltage command value Vr * During the period when the signal strength is less than that of a triangular wave TR, the gate control signal gate_rp corresponding to the R phase is set to "0".

[0039] As a result, the AC current Isr corresponding to the R phase gradually increases during the period when the gate control signal gate_rp is "0", and gradually decreases during the period when the gate control signal gate_rp is "1", as shown by the solid line in the lower part of Figure 5, under the voltage command value Vr. * It changes accordingly and is controlled on average to an alternating current as shown by the dashed line.

[0040] In this case, the compensated AC current detection signals CIsr, CIss, CIst and the compensated AC voltage detection signals CVsr, CVss, CVst output by the compensation control device 12 have a time resolution close to that of the analog signals detected by the current detection sensor 22 and the voltage detection sensor 24. Therefore, the converter control unit 25 can be configured to perform resampling at a timing synchronized with the peaks and troughs of the triangular wave TR (similar to Figure 4), enabling control calculations based on the average AC current excluding switching ripple. If the sampling process in the compensation control device 12 is performed at a frequency lower than twice the frequency of the triangular wave TR, and the timing of the sampling process does not coincide with the peaks and troughs of the triangular wave TR, then so-called aliasing occurs, which does not satisfy the sampling theorem, and an incorrect average AC current is detected. Therefore, by having the compensation control device 12 sample at a frequency higher than twice the frequency of the triangular wave TR as the carrier signal, it is possible to prevent the switching ripple from being amplified by the control calculation and causing instability in the operation of the converter.

[0041] As described above, according to this first embodiment, by simply attaching (interposing) a compensation control device 12 having a compensation calculation function unit 32 corresponding to the connected system to the power conversion system 10 to the power conversion device 11, the configuration of the power conversion device 11 can be easily adapted to the state of the connected system, and consequently, a highly reliable power conversion system with easily ensured stability can be provided.

[0042] [2] Second embodiment Figure 6 is a schematic block diagram of the power conversion system according to the second embodiment. The difference between the power conversion system of the second embodiment and the power conversion system of the first embodiment is that the gate command generation unit 44 outputs a synchronization signal SYNC synchronized with the calculation timing of the converter control unit 25 to the AD conversion unit 31 of the compensation control device via the interface unit 41, thereby controlling the operation timing of the compensation control device 12.

[0043] As a result, the compensation control device 12 can reliably synchronize with the actual operating timing of the power converter 21 to perform compensation control, enabling more accurate compensation control. Specifically, the synchronization signal SYNC is a signal synchronized with the peaks and troughs of the triangular wave TR as the carrier signal, and the AD conversion unit 31 of the compensation control device 12 can detect the average AC current excluding switching ripple by performing sampling processing at the black circles in the lower part of Figure 4 (peaks and troughs of the triangular wave TR) according to the synchronization signal SYNC. As a result, it is possible to prevent the converter's operation from becoming unstable due to amplification of switching ripple by control calculations.

[0044] In other words, with this second embodiment as well, by simply attaching (interposing) a compensation control device 12 having a compensation calculation function unit 32 corresponding to the connected system to the power system to which the power conversion system 10 is connected, the configuration of the power conversion device 11 can be used as is, and it is possible to easily respond to the state of the connected system in synchronization with the power conversion operation of the power conversion device 11, thereby providing a highly reliable power conversion system that easily ensures stability.

[0045] [3] Third embodiment Figure 7 is a schematic block diagram of the power conversion system according to the third embodiment. The power converter of the third embodiment differs from the power converter of the first embodiment in that it includes an AD conversion unit that performs analog / digital conversion of the AC current detection signals (=Isr, Iss, Ist) output from the current detection sensor 22 and the AC voltage detection signals (=Vsr, Vss, Vst) output from the voltage detection sensor 24 and outputs them to the interface unit as feedback data, and the compensation control device 12 performs compensation calculations on the AC current detection data and AC voltage detection data input from the interface unit and outputs them to the voltage / current control unit via the interface unit as compensation feedback data.

[0046] According to this third embodiment, since there is no need to provide an AD conversion unit and a DA conversion unit in the compensation control device, processing speed can be increased, the configuration of the compensation control device can be simplified, and the device cost can be reduced.

[0047] In this case, if the compensation control device 12 is not connected to the power converter 11, the converter control unit 25 may use the AC voltage detection signals (=Vsr, Vss, Vst) and / or AC current detection signals (=Isr, Iss, Ist) that have not undergone calculation processing by the compensation calculation function unit 32 for control calculations in the voltage / current control unit 43. For example, the interface unit may have a contact part that mechanically or electrically determines whether the compensation control device 12 is connected or not, and may be configured to automatically select which signal to use for control calculations electrically or by software based on the determination result of whether or not it is connected.

[0048] As described above, according to this third embodiment, by simply installing (interposing) a compensation control device 12 having a compensation calculation function unit 32 with a simpler configuration than those in the above embodiments to the power system to which the power conversion system 10 is connected, the configuration of the power conversion device 11 can be used as is, and it is possible to easily respond to the state of the connected power system in synchronization with the power conversion operation of the power conversion device 11, thereby providing a highly reliable power conversion system that easily ensures stability.

[0049] [4] Fourth Embodiment Figure 8 is a schematic block diagram of the power conversion system according to the fourth embodiment. In Figure 8, the same reference numerals are used for parts that are the same as those in the first embodiment of Figure 1.

[0050] The differences between the power conversion system of the fourth embodiment and the power conversion system of the first embodiment are that the fourth embodiment is equipped with output terminals that output AC current detection signals (=Isr, Iss, Ist) output from the current detection sensor 22 and AC voltage detection signals (=Vsr, Vss, Vst) output from the voltage detection sensor 24 to the compensation control device, and that the compensation control device 12X performs vibration frequency sensitivity reduction processing and virtual impedance control processing in parallel and outputs them to the interface section of the converter control unit.

[0051] The compensation control device 12 comprises an AD conversion unit 31, a compensation calculation function unit 32X, and a DA conversion unit 33. The AD conversion unit 31 performs analog-to-digital conversion of the AC current detection signals (=Isr, Iss, Ist) input from the current detection sensor 22 and the AC voltage detection signals (=Vsr, Vss, Vst) input from the voltage detection sensor 24, and outputs them to the compensation calculation function unit 32X.

[0052] The compensation calculation function unit 32X performs compensation calculations on the AC current detection signals (=Isr, Iss, Ist) and AC voltage detection signals (=Vsr, Vss, Vst) and outputs the compensation calculation results to the DA conversion unit 33.

[0053] The DA conversion unit 33 performs a digital-to-analog conversion of the compensation calculation result from the input compensation calculation function unit 32 and outputs it to the converter control unit 25 as compensated AC current detection signals CIsr, CIss, CIst and compensated AC voltage detection signals CVsr, CVss, CVst.

[0054] Here, the configuration of the compensation calculation function unit 32X of the compensation control device of the fourth embodiment will be described. Figure 9 is a block diagram illustrating the overview configuration of the compensation calculation function unit. The compensation calculation function unit 32X includes a resonance state detection unit 32A, a sensitivity reduction unit 32B, and a resonance suppression control unit 32C.

[0055] The resonance state detection unit 32A detects the vibration period (reciprocal of frequency) using a Fourier transform or counter on the detected values ​​of the AC voltages Vsr, Vss, and Vst, and extracts a vibration frequency fres or a vibration frequency band containing the vibration frequency fres, which is a state in which the harmonic amplitude exceeds a predetermined threshold within a predetermined frequency range.

[0056] In this case, the predetermined frequency range is set in advance to, for example, the range in which vibration frequency components are to be suppressed by the sensitivity reduction unit 32B. Alternatively, the predetermined frequency range may be set as, for example, a harmonic regulation range defined by some standard or a range in which a high risk of resonance occurrence has been identified through prior analysis.

[0057] Here, when the resonance state detection unit 32A detects a resonance state, it activates sensitivity reduction in the sensitivity reduction unit 32B, thereby reducing its sensitivity to the voltage / current control unit 43. The resonance state detection unit 32A detects the harmonic components of AC voltages Vsr, Vss, Vst or AC currents Isr, Iss, Ist. In this application, "A or B" is not limited to either A or B, but includes both A and B.

[0058] The resonance state detection unit 32A detects AC voltages Vsr, Vss, Vst or AC currents Isr, Iss, Ist, and detects vibration frequencies or vibration frequency bands within a predetermined frequency range where the harmonic amplitude exceeds a predetermined threshold. In the example in Figure 9, the resonance state detection unit 32A detects vibration frequencies or vibration frequency bands where the harmonic amplitude is greater than or equal to a predetermined threshold, based on the AC voltages Vsr, Vss, Vst. For example, the resonance state detection unit 32A identifies the frequency component with a large harmonic amplitude as the vibration frequency by performing a Fourier transform operation. Alternatively, the resonance state detection unit 32A may observe the vibration period of the AC voltages Vsr, Vss, Vst or AC currents Isr, Iss, Ist, and identify the vibration frequency by, for example, calculating the reciprocal of the vibration period.

[0059] The sensitivity reduction unit 32B reduces the sensitivity of the control in a frequency band that includes at least the vibration frequency. The sensitivity reduction unit 32B outputs AC currents with reduced sensitivity (AC currents Isr, Iss, Ist) and AC voltages with reduced sensitivity (AC voltages Vsr, Vss, Vst) to the voltage / current control unit 43. The sensitivity reduction unit 32B performs, for example, digital filtering on the AC voltages Vsr, Vss, Vst and AC currents Isr, Iss, Ist to attenuate components in the vibration frequency band fres.

[0060] Here, the digital filter may be a low-pass filter with a cutoff frequency lower than the vibration frequency, a notch filter that attenuates the frequency band including the vibration frequency, or a combination of these. When a low-pass filter and a notch filter are combined, the attenuation rate in the vibration frequency band can be increased compared to when they are not combined.

[0061] Some or all of the characteristics of the digital filter are dynamically adjusted to effectively attenuate the vibration frequency fres band extracted by the resonance state detection unit 32A. The cutoff frequency of the low-pass filter may be fixed to a value at least higher than the fundamental frequency. The sensitivity reduction unit 120 may dynamically change the sensitivity reduction characteristics of the voltage / current control unit 43X according to the vibration frequency fres. By reducing the sensitivity of the voltage / current control unit 43 to the vibration frequency fres band, amplification of the voltage / current components of the vibration frequency fres can be prevented. In other words, the sensitivity reduction unit has the effect of improving the stability of the converter control to at least a stable limit that does not lead to divergence.

[0062] The resonance suppression control unit 32C generates correction voltages VRr*, VRs*, and VRt* to correct the voltage command values ​​Vr1*, Vs1*, and Vt1*, which are operation commands to the power converter 21. In this embodiment, the correction voltages VRr*, VRs*, and VRt* function as a second compensation feedback signal. The second compensation feedback signal is an example of a compensation feedback signal. The resonance suppression control unit 32C generates correction voltages VRr*, VRs*, and VRt* based on the detected values ​​of the frequency band including at least the vibration frequency of the AC current.

[0063] More specifically, the resonance suppression control unit 32C generates correction voltages VRr*, VRs*, and VRt* by multiplying the signal, which has been processed to remove the fundamental frequency component from the detected AC current and contain only the harmonic components including the vibration frequency fres, by the characteristics of a virtual impedance.

[0064] In this case, the method for removing the fundamental frequency component is, for example, by processing with a notch filter that attenuates the band containing the fundamental frequency, or by digital processing that includes the function of a high-pass filter that effectively extracts the harmonic components. The resonance suppression control unit 32C may calculate the correction voltages VRr*, VRs*, and VRt* based on, for example, the AC current on a fixed coordinate axis that has been converted from three phases to two phases.

[0065] Here, we will explain the effects of providing the resonance suppression control unit 32C of the fourth embodiment. In the following explanation, the impedance viewed from the grid connection point GIP towards the power converter 21 is referred to as the converter impedance Zvsc. The converter impedance Zvsc is the impedance obtained by adding the characteristics of the power converter's control to the connection inductor Lvsc.

[0066] First, we will explain the impedance vector, phase margin, etc., of the power converter 11. Figure 10 shows an example of the impedance characteristics of the power converter according to the embodiment.

[0067] Figure 11 is a diagram showing an example of a vector diagram of the impedance of a power converter according to the fourth embodiment.

[0068] Here, as an example, we will explain a case where, due to the action of the sensitivity reduction unit 32B, the sensitivity of current control to the vibration frequency fres is sufficiently reduced, the transducer impedance is approximately equivalent to the interconnection inductance, and the transducer impedance Zvsc' can be considered to be approximately ωres·Lvsc.

[0069] Here, ωres is the angular frequency (=2π·fres) corresponding to the vibration frequency fres. At the vibration frequency fres, the amplitudes of the system impedance Zgrid and the transducer impedance Zvsc' are equal, and the phase difference is 180 degrees. That is, the phase margin is φm=0, which is the stability limit.

[0070] Here, when a correction component Zr with amplitude G·ωres·Lvsc and phase φr is added to the transducer impedance Zvsc', Figure 11 shows the phase margin Φ at the vibration frequency fres for the corrected transducer impedance Zvsc''. m This can be expressed by the following equation (1).

[0071]

number

[0072] In equation (1), G is a coefficient. The right-hand side of equation (1) is a value independent of the vibration frequency fres, provided that the coefficient G and phase φr are constants. This is because the amplitude of the correction component Zr is multiplied by the angular frequency ωres corresponding to the vibration frequency, so that the amplitude of the correction component Zr increases proportionally with increasing vibration frequency fres. This means that the effect of improving stability is obtained equally even when the vibration frequency fres changes.

[0073] Furthermore, if the amplitude of the correction component is G·ω0·Lvsc (where ω0 is a constant), the phase margin Φ at the vibration frequency fres is m This can be expressed by the following equation (2).

[0074]

number

[0075] The right-hand side of equation (2) decreases as ωres increases, so the phase margin decreases as the vibration frequency fres increases. This means that the effect of improving stability decreases as the vibration frequency fres increases.

[0076] To add the correction component Zr to the transducer impedance, the correction voltage can be obtained by multiplying the detected value, which includes at least the vibration frequency fres component of the AC current, by a characteristic corresponding to the amplitude of the correction component Zr. However, since the right-hand side of equation (1) takes a positive value when -90 degrees < φr < +90 degrees, care must be taken to ensure that the phase φr at the vibration frequency fres is within ±90 degrees in order to have a phase margin of φm > 0. This phase φr includes a series of phase characteristics from the detection of the AC current to the final output of the correction voltage.

[0077] Here, the correction component Zr can be considered a virtual impedance component realized in the transducer control, and its real part is a virtual resistance component. When the phase φr exceeds ±90 degrees, the real part becomes negative, and the correction component Zr functions as a negative resistance that amplifies vibrations. Therefore, when the phase φr exceeds ±90 degrees, the resonance suppression control may actually cause instability. For this reason, in this embodiment, in order to reduce the effect of resonance, the phase is controlled to be within ±90 degrees to ensure a phase margin.

[0078] As a result, the voltage / current control unit 43X corrects the command value of the AC voltage on the power converter 21 by adding (in parallel with the voltage / current control unit 43's processing) the corrected voltages VRr*, VRs*, and VRt*, which are the output signals of the resonance suppression control unit 32C that has undergone resonance suppression control processing as a second process (indicated as process 2 in Figure 8), to the command value of the AC voltage on the power converter 21, which has been calculated based on the output signal of the sensitivity reduction unit 32B that has undergone sensitivity reduction processing as a first process (indicated as process 1 in Figure 8) (input in series with the voltage / current control unit 43's processing).

[0079] In this case, the resonance state detection unit 32A functions as a vibration frequency detection unit that detects the vibration frequency or vibration frequency band in which the harmonic amplitude is maximum within a predetermined frequency range of AC voltage or current, and the resonance suppression control unit 32C adjusts the magnitude of the virtual impedance to increase with increasing vibration frequency.

[0080] Then, if the compensation control device 12X is not connected to the power converter 11, the converter control unit 25 uses the AC current detection signals (=Isr, Iss, Ist) and AC voltage detection signals (=Vsr, Vss, Vst) output from the voltage detection sensor 24, which have not undergone calculation processing by the compensation calculation function unit 32X, for control calculations in the voltage / current control unit 43X, and corrects the correction voltage VRr, which is the output signal of the resonance suppression control unit 32C, based on the second processing. * VRs * , VRt * Treat it as effectively zero.

[0081] As described above, according to this fourth embodiment, by simply installing (interposing) the compensation calculation function unit 32X having the resonance suppression control unit 32C into the power conversion system 10, the voltage / current control unit 43X can use the correction voltages VRr*, VRs*, and VRt* generated by multiplying the signal, which has been processed to remove the fundamental frequency component from the detected AC current and contain only the harmonic component including the vibration frequency fres, by the characteristics of a virtual impedance, for voltage and current control. This makes it possible to construct a highly reliable power conversion system that ensures stability with greater precision and ease without making significant changes to the basic configuration of the power conversion device 11.

[0082] [5] Modified examples of embodiments The compensation control device and converter control unit of this embodiment include a control device such as a CPU, a storage device such as ROM (Read Only Memory) or RAM, an external storage device such as a USB memory or SSD (Solid State Disk), a display device such as a display device, and some or all of an input device such as a keyboard or mouse, and thus has a hardware configuration that uses a normal computer.

[0083] The programs executed by the compensation control device and converter control unit of this embodiment are provided as files in an installable or executable format, recorded on a computer-readable recording medium such as a DVD (Digital Versatile Disk).

[0084] Furthermore, the program executed by the compensation control device and converter control unit of this embodiment may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. Alternatively, the program executed by the compensation control device and converter control unit of this embodiment may be provided or distributed via a network such as the Internet.

[0085] Furthermore, the programs for the compensation control device and the converter control device of this embodiment may be provided pre-installed in a ROM or the like.

[0086] 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 of the invention and its equivalents. [Explanation of symbols]

[0087] 10 Power Conversion Systems 11 Power converter 12, 12X compensation control device 21 Power Converters 22 Current detection sensor 23 interconnected inductors 24 Voltage detection sensors 25 Converter Control Unit 31 AD Conversion Unit 32, 32X compensation calculation function block 32A Resonance state detection unit 32B Sensitivity reduction section 32C Resonance Suppression Control Unit 33 DA Conversion Section 41 Interface section 42 AD Conversion Unit 43, 43X Voltage / Current Control Unit 44 Gate command generation unit 120 Sensitivity reduction section ACG AC commercial system ACIM system impedance CIsr Compensated AC Current Detection Signal CVsr Compensated AC Voltage Detection Signal Cgrid Equivalent Capacitance G coefficient GIP Grid Interconnection Point Isr, Iss, Ist AC current Lgrid Equivalent Inductance Lvsc Interconnected Inductor PSAC AC power supply SYNC synchronization signal TR triangle wave VRr * Correction voltage VR * Vs * , Vt * Voltage command value Vsr, Vss, Vst AC voltage ZGrid System Impedance Zr correction component Zvsc Transducer Impedance Zvsc' Transducer Impedance Zvsc” Converter Impedance fres vibration frequency gate, gate_rp gate control signal Φm Phase margin φr phase ωres angular frequency

Claims

1. A power conversion system having a power conversion device and a compensation control device, capable of mutually converting DC power and AC power, The power conversion device comprises a power converter including a switching element that can adjust the voltage or current of the AC power, an interface unit, a voltage / current control unit that generates and outputs a voltage command value for controlling the voltage or current of the AC power, and a gate command generation unit that generates a gate signal to be given to the switching element based on the voltage command value, and a converter control unit that gives an operation command to the switching element. The compensation control device is detachably attached to the power converter via the interface unit, and compensates the feedback signals of the AC power voltage and / or AC power current to the voltage / current control unit, and outputs them as a compensation feedback signal to the converter control unit. The converter control unit can select the signal used in the voltage / current control unit to calculate the voltage command value from the feedback signal based on the voltage or current of the AC power and the compensation feedback signal output by the compensation control unit. Power conversion system.

2. A power conversion system having a power conversion device and a compensation control device, capable of mutually converting DC power and AC power, The power conversion device comprises a power converter including a switching element that can adjust the voltage or current of the AC power, an interface unit, a voltage / current control unit that generates and outputs a voltage command value for controlling the voltage or current of the AC power, and a gate command generation unit that generates a gate signal to be given to the switching element based on the voltage command value, and a converter control unit that gives an operation command to the switching element. The compensation control device is detachably attached to the power converter via the interface unit, and compensates the feedback signals of the AC power voltage and / or AC power current to the voltage / current control unit, and outputs them as a compensation feedback signal to the converter control unit. The converter control unit, when the compensation control device is not connected to the power converter, uses the feedback signal based on the voltage or current of the AC power to calculate the voltage command value in the voltage / current control unit. Power conversion system.

3. The compensation control device includes a sensitivity reduction unit that reduces the sensitivity of a predetermined frequency band in the feedback signal and outputs it as the compensation feedback signal. The compensation feedback signal is input in series to the calculation process of the voltage command value in the voltage / current control unit. A power conversion system according to claim 1 or claim 2.

4. The compensation control device includes a resonance state detection unit that detects harmonic components contained in the voltage or current of the AC power, and the sensitivity reduction unit outputs the compensation feedback signal based on the harmonic components detected by the resonance state detection unit. The power conversion system according to claim 3.

5. The aforementioned sensitivity reduction unit is capable of processing digital signals, The compensation control device is provided in front of the sensitivity reduction unit and includes an AD conversion unit that performs analog / digital conversion of the feedback signal, A DA conversion unit is provided downstream of the sensitivity reduction unit, which performs digital-to-analog conversion of the output of the sensitivity reduction unit and outputs it as the compensation feedback signal. In either one or both of the following: The power conversion system according to claim 3.

6. The compensation control device includes a resonance suppression control unit that generates a correction voltage based on the voltage or current of the AC power, The correction voltage is output to the converter control unit as a second compensation feedback signal. The voltage and current control unit adds the second compensation feedback signal in parallel to the voltage command value obtained by the calculation process to obtain a new voltage command value. A power conversion system according to claim 1 or claim 2.

7. The compensation control device includes a resonance state detection unit that detects harmonic components contained in the voltage or current of the AC power, and the resonance suppression control unit outputs the second compensation feedback signal based on the harmonic components detected by the resonance state detection unit. The power conversion system according to claim 6.

8. The resonance state detection unit includes a vibration frequency detection unit that detects the vibration frequency or vibration frequency band in which the harmonic amplitude is maximum within a predetermined frequency range of the voltage or current of the AC power. The resonance suppression control unit generates the correction voltage by multiplying the harmonic components by a virtual impedance, and adjusts the magnitude of the virtual impedance to increase with increasing vibration frequency. The power conversion system according to claim 7.

9. The voltage / current control unit adds the second compensation feedback signal generated by the resonance suppression control unit to the voltage command value calculated based on the compensation feedback signal to obtain a new corrected voltage command value. The power conversion system according to claim 6.

10. The gate command generation unit generates the gate signal by comparing the modulated wave based on the voltage command value with the triangular wave carrier. A synchronization signal corresponding to the timing of the peak and / or bottom of the triangular wave carrier can be output to the compensation control device. The compensation control device samples an analog signal based on the voltage and / or current of the AC power based on the synchronization signal. A power conversion system according to claim 1 or claim 2.

11. The compensation control device samples an analog signal based on the voltage and / or current of the AC power at a frequency at least twice the switching frequency of the switching element. A power conversion system according to claim 1 or claim 2.

12. A power converter capable of converting DC power to AC power comprises a power converter including a switching element that can adjust the voltage or current of the AC power, and a converter control unit having an interface unit that gives operation commands to the switching element, wherein the power converter is detachably attached to the power converter via the interface unit, and cooperates with the power converter to compensate the detected feedback signals of the voltage and / or current of the AC power and output them as a compensated feedback signal to the converter control unit via the interface unit, When the compensation control device is connected to the power converter, the compensation feedback signal is used for the control calculation of the converter control unit. If the compensation control device is not connected to the power converter, the feedback signal based on the voltage of the AC power or the current of the AC power is used for the control calculation. Compensation control device.

13. The interface portion of the power converter has a contact portion capable of mechanically or electrically determining whether or not the compensation control device is connected, The presence or absence of the connection is determined by the contact portion. The compensation control device according to claim 12.

14. The converter control unit is configured to cooperate with the power converter so that it can select the signal used for the control calculation from the feedback signal based on the voltage of the AC power or the current of the AC power and the compensation feedback signal, The compensation control device according to claim 12.

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