Control device and control method for grid-forming inverter
The control device for grid-forming inverters addresses the challenge of continuous operation during disturbances by switching to one-pulse control, reducing switching operations and heat generation, thus minimizing semiconductor element damage and downsizing the inverter.
Patent Information
- Application Number
- JP2024038792
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-03-13
- Publication Date
- 2025-09-29
AI Technical Summary
Grid-forming inverters face challenges in maintaining continuous operation during system disturbances due to increased current and heat generation in semiconductor switching elements, leading to potential damage and requiring larger devices and higher component costs.
A control device for grid-forming inverters that switches from normal PWM control to one-pulse control when current or active power thresholds are exceeded, reducing switching operations and heat generation by using one-pulse modulation or low-frequency triangular waves.
Enables continuous operation without damaging semiconductor switching elements, reducing their number and cooling mechanism size, while maintaining power output.
Smart Images
Figure 2025139772000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a control device and an operation method for a grid-forming inverter (hereinafter also referred to as a GFM inverter). [Background technology]
[0002] With the large-scale introduction of renewable energy sources, GFM inverters, which supply inertia to the grid, are attracting attention. Because GFM inverters are voltage-controlled inverters, their current output easily increases during grid disturbances, causing losses in semiconductor switching elements such as IGBTs to generate heat. Generally, inverters are damaged when the elements heat up above a certain level, so operation is stopped by a protection device. The purpose of introducing GFM inverters is to improve the stability of the power supply capacity of distributed power systems, so it is necessary to continue operation as long as possible before the device reaches its protection level.
[0003] Incidentally, with regard to the control of the inertial force inverter, techniques have been disclosed in the past, for example, as described in Non-Patent Documents 1 and 2. [Prior art documents] [Non-patent literature]
[0004] [Non-Patent Document 1] Kenichi Sakimoto, Tomofumi Miura, and Toshifumi Ise, "Static Control of Power Systems Including Inverter-Connected Distributed Generators Using Virtual Synchronous Generators," Journal of Electrical Engineering B, Vol. 132, No. 4, pp. 341-349, 2012 [Non-patent document 2] Hideto Kushida, Tomofumi Miura, "Overcurrent Suppression of Energy Storage Devices Using Virtual Synchronous Generator Control in Small-Scale Power Systems," Semiconductor Power Conversion / Motor Drive Joint Research Meeting, January 27, 2022, SPC-22-044, pp. 25-30 Summary of the Invention [Problem to be solved by the invention]
[0005] A GFM inverter is a device designed to compensate for disturbances in three-phase power supplies, and is required to continue operation, such as maintaining output power, even when the system becomes unstable and reaches an overload (overcurrent) range.
[0006] However, because semiconductor switching elements generally have little margin in their voltage and current ratings, the current rating can be increased by selecting semiconductor switching elements with a large rated current when selecting the main circuit of the GFM inverter, or by arranging semiconductor switching elements in parallel.However, in this case, problems arise such as an increase in the size of the GFM inverter device and an increase in component prices due to an increase in the number of semiconductor switching elements and an increase in the size of the semiconductor cooling mechanism.
[0007] The techniques described in Non-Patent Documents 1 and 2 have a problem in that they cannot continue operation when an output higher than the specified current / load is required.
[0008] The present invention is devised to solve the above-mentioned problems, and its object is to provide a control device for a grid-forming inverter that reduces the number of switching operations of the grid-forming inverter during a disturbance in the system (three-phase power supply) and enables continuous operation without damaging the semiconductor switching elements. [Means for solving the problem]
[0009] The grid forming inverter control device according to claim 1 for solving the above problem comprises: A control device for a grid forming inverter connected in parallel to a three-phase power supply and supplying inertia, comprising: an output voltage command generation unit that generates an output voltage command for the grid-forming inverter based on an output voltage amplitude of the grid-forming inverter obtained by performing control based on a reactive power command and an output phase of the grid-forming inverter obtained by performing control that simulates the motion characteristics of a synchronous generator using a system frequency and the active power of the grid-forming inverter; a current comparison unit that compares the output current of the grid forming inverter with a set output current threshold; a one-pulse control block that generates a one-pulse modulation voltage signal for outputting a one-pulse gate signal in a half cycle of a sine wave of an output voltage command of the grid forming inverter, using the output voltage amplitude of the grid forming inverter; a triangular wave generating unit that generates a triangular wave signal; a carrier selection unit that selects the voltage signal for one-pulse modulation generated by the one-pulse control block as a carrier signal when the comparison result of the current comparison unit is that the output current is greater than the output current threshold, and selects the triangular wave signal generated by the triangular wave generation unit as a carrier signal when the output current is less than the output current threshold, The output voltage command generated by the output voltage command generating unit and the carrier signal selected by the carrier selecting unit are compared to generate a gate command signal for the grid forming inverter.
[0010] The grid forming inverter control device according to claim 2 comprises: A control device for a grid forming inverter connected in parallel to a three-phase power supply and supplying inertia, comprising: an output voltage command generation unit that generates an output voltage command for the grid-forming inverter based on an output voltage amplitude of the grid-forming inverter obtained by performing control based on a reactive power command and an output phase of the grid-forming inverter obtained by performing control that simulates the motion characteristics of a synchronous generator using a system frequency and the active power of the grid-forming inverter; a first power comparator that compares the active power of the grid forming inverter with a set first active power threshold; a one-pulse control block that generates a one-pulse modulation voltage signal for outputting a one-pulse gate signal in a half cycle of a sine wave of an output voltage command of the grid forming inverter, using the output voltage amplitude of the grid forming inverter; a triangular wave generating unit that generates a triangular wave signal; a first carrier selection unit that selects, as a carrier signal, the voltage signal for one-pulse modulation generated by the one-pulse control block when the comparison result of the first power comparison unit is that the active power is greater than a first active power threshold, and that selects, as a carrier signal, the triangular wave signal generated by the triangular wave generation unit when the comparison result of the first power comparison unit is that the active power is less than the first active power threshold; The output voltage command generated by the output voltage command generating unit and the carrier signal selected by the first carrier selecting unit are compared to generate a gate command signal for the grid forming inverter.
[0011] The grid forming inverter control device according to claim 3 is the control device according to claim 2, the triangular wave generating unit generates a triangular wave signal of a first frequency and a triangular wave signal of a second frequency lower than the first frequency; a second power comparator that compares the active power of the grid forming inverter with a second active power threshold that is set to be smaller than the first active power threshold; a second carrier selection unit that selects the triangular wave signal of the second frequency when the comparison result of the second power comparison unit is that the active power is greater than a second active power threshold, and that selects the triangular wave signal of the first frequency when the active power is less than the second active power threshold, When the comparison result of the first power comparison unit is that the active power is less than the first active power threshold, the first carrier selection unit selects the triangular wave signal selected by the second carrier selection unit as the carrier signal instead of the triangular wave signal generated by the triangular wave generation unit.
[0012] The grid forming inverter control method according to claim 4 comprises: 1. A method for controlling a grid forming inverter connected in parallel to a three-phase power supply and providing inertia, comprising: an output voltage command generating unit generating an output voltage command for the grid-forming inverter based on an output voltage amplitude of the grid-forming inverter obtained by performing control based on a reactive power command and an output phase of the grid-forming inverter obtained by performing control simulating the motion characteristics of a synchronous generator using a system frequency and the active power of the grid-forming inverter; a current comparison unit comparing the output current of the grid forming inverter with a set output current threshold; a step in which a one-pulse control block uses an output voltage amplitude of the grid forming inverter to generate a one-pulse modulation voltage signal for outputting a gate signal of one pulse in a half cycle of a sine wave of an output voltage command of the grid forming inverter; a carrier selection unit selecting the voltage signal for one-pulse modulation generated by the one-pulse control block as a carrier signal when the comparison result of the current comparison unit is that the output current is greater than the output current threshold, and selecting a triangular wave signal as a carrier signal when the output current is less than the output current threshold; a gate signal generating unit comparing the output voltage command generated by the output voltage command generating unit with the carrier signal selected by the carrier selecting unit to generate a gate command signal for the grid forming inverter; The present invention is characterized by the following features. [Effects of the Invention]
[0013] (1) According to the inventions described in claims 1 to 4, when a disturbance occurs in the grid (three-phase power supply), it is possible to switch from normal PWM control to one-pulse control, thereby reducing the number of switching operations and enabling continuous operation without damaging the semiconductor switching elements. As a result, it is possible to reduce the number of semiconductor switching elements required for the grid forming inverter and to downsize the cooling mechanism. (2) According to the inventions set forth in claims 1 and 4, the same effect as that of (1) can be obtained when the output current of the grid forming inverter increases. (3) According to the invention described in claim 2, the same effect as that described in (1) above can be obtained when the output power of the grid forming inverter is increased. (4) According to the invention described in claim 3, when the active power of the grid-forming inverter exceeds a second active power threshold that is smaller than the first active power threshold, a triangular wave signal of a second frequency that is lower than the first frequency is selected as the carrier signal, so that the same effect as that described in (1) can be obtained even during normal PWM control.
[0014] In addition, when the active power of the grid-forming inverter exceeds the first active power threshold, which is greater than the second active power threshold, the voltage signal for one pulse modulation is selected as the carrier signal, thereby achieving the same effect as (1) above. [Brief explanation of the drawings]
[0015] [Figure 1] 1 is a diagram showing the overall system configuration to which a control device of the present invention is applied; [Figure 2] Control block diagram of the GFM inverter. [Figure 3] FIG. 1 is a control block diagram of a first embodiment of the present invention. [Figure 4] FIG. 4 is a waveform diagram when switching from PWM to one-pulse control in the present invention. [Figure 5] FIG. 10 is a control block diagram of a second embodiment of the present invention. [Figure 6] FIG. 10 is a control block diagram of a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION
[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. Figure 1 shows the overall system configuration, in which 1 is a three-phase power supply that supplies power to a load 2, and a GFM inverter 3 (a three-phase inverter and a necessary filter circuit) that supplies inertia is connected in parallel to the three-phase power supply 1.
[0017] Here, a synchronous generator is assumed as the three-phase power supply 1. The DC power supply of the GFM inverter 3 is Vdc, the output voltage is Vo, the output current is Io, the output active power is P, and the output reactive power is Q.
[0018] Figure 2 shows a control block diagram of the GFM inverter 3. In Figure 2, reference numeral 11 denotes a VSG (Virtual Synchronous Generator) control unit that performs control simulating the motion characteristics of a synchronous generator. The VSG control unit 11 generates the output phase θm of the GFM inverter based on the grid frequency ωn and available power P.
[0019] Reference numeral 12 denotes a reactive power control block, which performs control based on the reactive power command Qref and generates the output voltage amplitude E of the GFM inverter. Reference numeral 13 denotes an output voltage command generation unit that generates the output voltage command Vref of the GFM inverter by substituting the output voltage amplitude E and the output phase θm into equation (1).
[0020]
number
[0021] Vu, Vv, and Vw are output voltage commands for the U, V, and W phases, respectively.
[0022] Reference numeral 14 denotes a triangular wave generating unit that generates a triangular wave signal (carrier signal).
[0023] Reference numeral 15 denotes a PWM (Pulse Width Modulation) block that compares the output voltage command Vref with a triangular wave signal to generate a gate command Gate for the GFM inverter.
[0024] The GFM inverter 3 is driven by a gate command Gate generated by a PWM block 15 . [Example]
[0025] Heat generation in semiconductor switching elements is proportional to the current value and the number of switching operations. In this first embodiment, in order to suppress heat generation, when the output current Io exceeds the output current threshold Ith, PWM is switched to one-pulse control, which has fewer switching operations. Here, one-pulse control is a control that outputs only one pulse per half cycle of a sine wave. When the absolute value of the output current Io falls below the threshold Ith, normal PWM is restored.
[0026] Figure 3 shows a GFM control block diagram in Example 1. Figure 3 differs from Figure 2 in that it additionally includes a one-pulse control block 16 that uses the output voltage amplitude E of the GFM inverter to generate one-pulse control commands ±M (voltage signals for one-pulse modulation) for outputting a gate signal of one pulse in each sine wave half cycle of the output voltage command of the GFM inverter, a current comparison unit 17 that compares the output current of the GFM inverter (absolute value |Io| of Io) with a set output current threshold Ith, and a carrier selection unit 18 that selects the one-pulse control commands ±M generated by the one-pulse control block 16 as a carrier signal when the comparison result of the current comparison unit 17 is that the output current is greater than the output current threshold, and selects the triangular wave signal generated by the triangular wave generation unit 14 as a carrier signal when the output current is less than the output current threshold. The other components are configured in the same way as in Figure 2.
[0027] The one-pulse control block 16 uses the output voltage amplitude E of the GFM inverter to calculate a one-pulse control command (M) so that the half-wave average value of the output voltage command Vref and the one-pulse output half-wave average value match. Since a sine wave is positive-negative symmetrical, the one-pulse control command M is also positive-negative symmetrical, so it is set to ±M.
[0028] Figure 4 shows the gate waveforms when switching from PWM to one-pulse control using the configuration in Figure 3. The upper part of Figure 4 shows the output voltage amplitude E of the GFM inverter, the one-pulse control commands +M and -M, the U-phase output voltage command Vu, and the triangular wave signal, while the lower part of Figure 4 shows the gate waveforms. The V-phase output voltage command Vv and W-phase output voltage command Vw are also the same as in Figure 4.
[0029] In Figures 3 and 4, when the output current Io of the GFM inverter does not exceed the output current threshold Ith, the carrier selection unit 18 selects the triangular wave signal of the triangular wave generation unit 14, and the PWM block 15 outputs a gate signal that is the result of comparing the U-phase output voltage command Vu with the triangular wave signal.
[0030] When the output current Io of the GFM inverter exceeds the output current threshold Ith, the carrier selection unit 18 switches the selection to the ±M side of the one-pulse control command of the one-pulse control block 16, and a gate signal with only one pulse per half cycle of the sine wave is output from the PWM block 15. This reduces the number of switching times of the semiconductor switching elements.
[0031] As described above, according to the first embodiment, when the output current Io exceeds the threshold value Ith, the control switches to one-pulse control, which reduces the number of switching operations compared to PWM, and therefore reduces heat generation in the semiconductor switching elements even when the current increases. This allows the inertia force inverter to continue operating without damaging the semiconductor switching elements. As a result, it is possible to reduce the number of semiconductor switching elements required for the GFM inverter and to downsize the cooling mechanism. [Example]
[0032] Heat generation in semiconductor switching elements is proportional to the active power value and the number of switching operations. In this second embodiment, in order to suppress heat generation, when the active power P exceeds the active power threshold Pth, PWM is switched to one-pulse control, which has fewer switching operations. Here, one-pulse control is a control that outputs only one pulse per half cycle of a sine wave. When the absolute value of the output power P falls below the threshold Pth, normal PWM is restored.
[0033] Figure 5 shows a GFM control block diagram in Example 2. In Figure 5, only the judgment criteria of the carrier selection unit are different from those in Figure 3. Instead of the current comparison unit 17 and carrier selection unit 18 in Figure 3, a first power comparison unit 27 that compares the active power of the GFM inverter (the absolute value of P |P|) with a set first active power threshold Pth, and a first carrier selection unit 28 that selects the one-pulse control command ±M generated in the one-pulse control block 16 as the carrier signal when the comparison result of the first power comparison unit 27 is that the active power is greater than the first active power threshold, and selects the triangular wave signal generated in the triangular wave generation unit 14 as the carrier signal when the active power is less than the first active power threshold, are provided. Other parts are configured in the same way as in Figure 3.
[0034] The gate waveform when switching from PWM to one-pulse control in the second embodiment is the same as that in FIG.
[0035] When the active power of the GFM inverter does not exceed the first active power threshold Pth, the carrier selection unit 28 selects the triangular wave signal of the triangular wave generation unit 14, and the PWM block 15 outputs a gate signal that is the result of comparing the output voltage command Vref with the triangular wave signal.
[0036] When the active power of the GFM inverter exceeds the first active power threshold Pth, the first carrier selector 28 switches the selection to the ±M side of the one-pulse control command of the one-pulse control block 16, and a gate signal of only one pulse per half cycle of the sine wave is output from the PWM block 15. This reduces the number of switching operations of the semiconductor switching elements.
[0037] As described above, according to the second embodiment, when the active power exceeds the threshold value Pth, the control switches to one-pulse control, which reduces the number of switching operations compared to PWM, and therefore reduces heat generation in the semiconductor switching elements even when power increases. This allows the inertia force inverter to continue operating without damaging the semiconductor switching elements. As a result, it is possible to reduce the number of semiconductor switching elements required for the GFM inverter and to downsize the cooling mechanism. [Example]
[0038] In this third embodiment, in addition to switching to one-pulse control when the active power exceeds the first active power threshold as in the second embodiment, the control is configured to select a low-frequency triangular wave signal to reduce the number of switching operations even during normal PWM control when the active power exceeds a second active power threshold set smaller than the first threshold.
[0039] Figure 6 shows a GFM control block diagram in the third embodiment. In Figure 6, the same parts as in Figure 5 are designated by the same reference numerals, but the configuration differs from Figure 5 as follows.
[0040] The triangular wave generating section includes a triangular wave generating section 14a that generates a triangular wave signal of a first frequency, and a triangular wave generating section 14b that generates a triangular wave signal of a second frequency that is lower than the first frequency.
[0041] 37 is a second power comparator that compares the active power of the GFM inverter with a second active power threshold Pth12 that is set to be smaller than the first active power threshold Pth.
[0042] Reference numeral 38 denotes a second carrier selection unit that selects a triangular wave signal of the second frequency from the triangular wave generation unit 14b when the comparison result of the second power comparison unit 37 is that the active power is greater than the second active power threshold Pth12, and that selects a triangular wave signal of the first frequency from the triangular wave generation unit 14a when the active power is less than the second active power threshold Pth12.
[0043] When the comparison result of the first power comparator 27 is that the active power is greater than the first active power threshold Pth, the first carrier selector 28 selects the one-pulse control command ±M generated by the one-pulse control block 16 as the carrier signal, and when the active power is less than the first active power threshold Pth, the first carrier selector 28 selects the triangular wave signal selected by the second carrier selector 38 as the carrier signal.
[0044] In FIG. 6, when the active power of the GFM inverter satisfies the condition that the active power <Pth12 < Pth, the first carrier selection unit 28 selects the second carrier selection unit 38 side, and the second carrier selection unit 38 selects the triangular wave signal with the first frequency (the higher frequency) of the triangular wave generation unit 14a. Therefore, the PWM block 15 outputs a gate signal which is the comparison result between the output voltage command Vref and the triangular wave signal with the first frequency.
[0045] Also, when the active power of the GFM inverter satisfies the condition that the active power > Pth12 < Pth, the first carrier selection unit 28 selects the second carrier selection unit 38 side, and the second carrier selection unit 38 selects the triangular wave signal with the second frequency (the lower frequency) of the triangular wave generation unit 14b. Therefore, the PWM block 15 outputs a gate signal which is the comparison result between the output voltage command Vref and the triangular wave signal with the second frequency.
[0046] Also, when the active power of the GFM inverter satisfies the condition that the active power > Pth > Pth12, the first carrier selection unit 28 selects the one-pulse control command ±M of the one-pulse control block 16. Therefore, the PWM block 15 outputs a gate signal with only one pulse in a half cycle of the sine wave.
[0047] As described above, according to the third embodiment, the same effect as that of the second embodiment can be obtained when the power increases. Furthermore, even during normal PWM control, the carrier signal can be switched to a low-frequency one to reduce the switching frequency of the semiconductor switching element.
Explanation of symbols
[0048] 1... Three-phase power supply 2... Load 3... GFM inverter 11... VSG control unit 12... Reactive power control block 13... Output voltage command generation unit 14, 14a, 14b... Triangular wave generation unit 15... PWM block 16... One-pulse control block 17... Current comparison unit 18...Career Selection Department 27...First power comparison unit 28...First Career Selection Section 37...Second power comparison unit 38...Second Career Selection Section
Claims
1. A control device for a grid forming inverter connected in parallel to a three-phase power supply and supplying inertia, comprising: an output voltage command generation unit that generates an output voltage command for the grid-forming inverter based on an output voltage amplitude of the grid-forming inverter obtained by performing control based on a reactive power command and an output phase of the grid-forming inverter obtained by performing control that simulates the motion characteristics of a synchronous generator using a system frequency and the active power of the grid-forming inverter; a current comparison unit that compares the output current of the grid forming inverter with a set output current threshold; a one-pulse control block that generates a one-pulse modulation voltage signal for outputting a one-pulse gate signal for one half cycle of a sine wave of an output voltage command of the grid forming inverter, using the output voltage amplitude of the grid forming inverter; a triangular wave generating unit that generates a triangular wave signal; a carrier selection unit that selects the voltage signal for one-pulse modulation generated by the one-pulse control block as a carrier signal when the comparison result of the current comparison unit is that the output current is greater than the output current threshold, and selects the triangular wave signal generated by the triangular wave generation unit as a carrier signal when the comparison result of the current comparison unit is that the output current is less than the output current threshold, a control device for a grid forming inverter, characterized in that the output voltage command generated by the output voltage command generation unit and the carrier signal selected by the carrier selection unit are compared to generate a gate command signal for the grid forming inverter.
2. A control device for a grid forming inverter connected in parallel to a three-phase power supply and supplying inertia, comprising: an output voltage command generation unit that generates an output voltage command for the grid-forming inverter based on an output voltage amplitude of the grid-forming inverter obtained by performing control based on a reactive power command and an output phase of the grid-forming inverter obtained by performing control that simulates the motion characteristics of a synchronous generator using a system frequency and the active power of the grid-forming inverter; a first power comparator that compares the active power of the grid forming inverter with a set first active power threshold; a one-pulse control block that generates a one-pulse modulation voltage signal for outputting a one-pulse gate signal for one half cycle of a sine wave of an output voltage command of the grid forming inverter, using the output voltage amplitude of the grid forming inverter; a triangular wave generating unit that generates a triangular wave signal; a first carrier selection unit that selects, as a carrier signal, the voltage signal for one-pulse modulation generated by the one-pulse control block when the comparison result of the first power comparison unit is that the active power is greater than a first active power threshold, and that selects, as a carrier signal, the triangular wave signal generated by the triangular wave generation unit when the comparison result of the first power comparison unit is that the active power is less than the first active power threshold; a control device for a grid forming inverter, characterized in that the output voltage command generated by the output voltage command generation unit and the carrier signal selected by the first carrier selection unit are compared to generate a gate command signal for the grid forming inverter.
3. the triangular wave generating unit generates a triangular wave signal of a first frequency and a triangular wave signal of a second frequency lower than the first frequency, a second power comparator that compares the active power of the grid forming inverter with a second active power threshold that is set to be smaller than the first active power threshold; a second carrier selection unit that selects the triangular wave signal of the second frequency when the comparison result of the second power comparison unit is that the active power is greater than a second active power threshold, and that selects the triangular wave signal of the first frequency when the active power is less than the second active power threshold, 3. The grid-forming inverter control device according to claim 2, wherein when the comparison result of the first power comparison unit is that the active power is less than the first active power threshold, the first carrier selection unit selects the triangular wave signal selected by the second carrier selection unit as the carrier signal instead of the triangular wave signal generated by the triangular wave generation unit.
4. 1. A method for controlling a grid forming inverter connected in parallel to a three-phase power supply and providing inertia, comprising: an output voltage command generating unit generating an output voltage command for the grid-forming inverter based on an output voltage amplitude of the grid-forming inverter obtained by performing control based on a reactive power command and an output phase of the grid-forming inverter obtained by performing control simulating the motion characteristics of a synchronous generator using a system frequency and the active power of the grid-forming inverter; a current comparison unit comparing the output current of the grid forming inverter with a set output current threshold; a step in which a one-pulse control block generates a one-pulse modulation voltage signal for outputting a gate signal of one pulse in a half cycle of a sine wave of an output voltage command of the grid forming inverter, using the output voltage amplitude of the grid forming inverter; a carrier selection unit selecting the voltage signal for one-pulse modulation generated by the one-pulse control block as a carrier signal when the comparison result of the current comparison unit is that the output current is greater than the output current threshold, and selecting a triangular wave signal as a carrier signal when the output current is less than the output current threshold; a gate signal generating unit comparing the output voltage command generated by the output voltage command generating unit with the carrier signal selected by the carrier selecting unit to generate a gate command signal for the grid forming inverter; A method for controlling a grid forming inverter, comprising: