A power regulation system for multi-level inverter

Abstract

The present invention relates to the field of power electronic control technology, and specifically discloses a power regulation system for a multi-stage inverter. By arranging a dynamic compensation capacitor between a front-stage circuit and an inverter circuit, power fluctuations of the multi-stage inverter are eliminated by dynamic charging and discharging, thereby ensuring that the multi-stage inverter is in a stable operating state. In particular, a control unit connected to the front-stage circuit is also provided, which can accurately and reliably determine the AC fluctuating voltage required to be output by the front-stage circuit to match the dynamic compensation capacitor, and control the front-stage circuit to provide a suitable AC fluctuating voltage for the dynamic compensation capacitor, thereby further reducing the instantaneous power demand of the front-stage circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic control, in particular to a power regulation system of a multi-level inverter. Background Art

[0002] With the continuous development of the power electronics industry, multi-level inverters are becoming more and more widely used. Generally speaking, multi-level inverters can be divided into a front-stage DCDC circuit and a back-stage DCAC inverter circuit. In multi-level inverters, due to load fluctuations, the instantaneous power peak is twice the average power, which forces the front-stage circuit to be designed according to the peak power, resulting in redundant capacitance of the front-stage circuit components and relatively high costs. Currently, related technologies improve this by adding an LC filter circuit between the front-stage and back-stage circuits. Although this can partially smooth the current, since the inverter usually operates at industrial frequency, the filter inductors and capacitors in the LC filter circuit are large and have the risk of resonance. This can easily lead to voltage loss between the front-stage and back-stage circuits, causing power fluctuations in the multi-level inverter. Summary of the Invention

[0003] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the present invention proposes a power regulation system for a multi-level inverter, which can eliminate power fluctuations of the multi-level inverter.

[0004] In a first aspect, an embodiment of the present invention provides a power regulation system for a multi-level inverter, wherein the multi-level inverter includes a front-stage circuit for outputting a DC average voltage and an inverter circuit for outputting inverter power, and the power regulation system includes:

[0005] a dynamic compensation capacitor connected in parallel between the front-stage circuit and the inverter circuit, for dynamically charging and discharging to eliminate power fluctuations of the multi-stage inverter, thereby reducing the instantaneous power demand of the front-stage circuit;

[0006] a control unit, connected to the front-stage circuit and the inverter circuit, respectively, for determining the AC fluctuating voltage required to be output by the front-stage circuit and matching the dynamic compensation capacitor, and controlling the front-stage circuit to output the AC fluctuating voltage;

[0007] The frequency of the AC fluctuating voltage is twice the frequency of the output voltage of the inverter circuit, the phase of the AC fluctuating voltage is twice the phase of the output voltage, and the amplitude of the AC fluctuating voltage can be dynamically adjusted.

[0008] Optionally, in one embodiment of the present invention, the control unit specifically determines the AC fluctuating voltage required to be output by the pre-stage circuit and matched to the dynamic compensation capacitor in the following manner:

[0009] Acquiring an output voltage waveform of the inverter circuit, and determining a voltage effective value, an angular frequency, and phase information of the inverter circuit according to the output voltage waveform;

[0010] Acquiring an output current waveform of the inverter circuit, and determining an effective current value of the inverter circuit according to the output current waveform;

[0011] Obtaining the average DC voltage output by the preceding circuit and the capacitance of the dynamic compensation capacitor;

[0012] The AC fluctuating voltage required to be output by the front-stage circuit and matching the dynamic compensation capacitor is determined according to the voltage effective value, the angular frequency, the phase information, the current effective value, the DC average voltage and the capacitance.

[0013] Optionally, in one embodiment of the present invention, the control unit specifically controls the front-stage circuit to output the AC fluctuating voltage in the following manner:

[0014] When the front-stage circuit adopts an output programmable circuit, an AC fluctuating waveform is injected into the DC average voltage, wherein the frequency of the AC fluctuating waveform is twice the frequency of the output voltage waveform, the phase of the AC fluctuating waveform is twice the phase of the output voltage waveform, and the amplitude of the AC fluctuating waveform can be dynamically adjusted;

[0015] reading an output current fluctuation amplitude of the preceding circuit, and continuously controlling the output current fluctuation amplitude until a target current fluctuation condition is met, wherein the target current fluctuation condition is that the output current fluctuation amplitude is less than or equal to a preset current fluctuation amplitude;

[0016] The AC ripple waveform that satisfies the target current ripple condition is output as the AC ripple voltage, and the front-stage circuit is controlled to output the AC ripple voltage based on the DC average voltage.

[0017] Optionally, in one embodiment of the present invention, the control unit specifically controls the front-stage circuit to output the AC fluctuating voltage in the following manner:

[0018] When the front-stage circuit adopts an output voltage closed-loop control circuit and the front-stage circuit includes a closed-loop control unit, the instantaneous value of the AC voltage of the front-stage circuit is superimposed on the AC fluctuating voltage given by the control unit, thereby controlling the closed-loop control unit to keep the instantaneous value of the AC voltage consistent with the AC fluctuating voltage based on a PID algorithm;

[0019] The front-stage circuit is controlled to output the AC fluctuating voltage based on the DC average voltage.

[0020] Optionally, in one embodiment of the present invention, the control unit specifically controls the front-stage circuit to output the AC fluctuating voltage in the following manner:

[0021] When the front-stage circuit adopts a constant voltage and current limiting output function circuit, the control unit obtains the output current of the front-stage circuit, and when the output current of the front-stage circuit is greater than a preset output current value, controls the front-stage circuit to output at the preset output current value; otherwise, controls the front-stage circuit to output at a constant voltage;

[0022] reading a real-time current limiting state of the preceding circuit, and adaptively adjusting the preset output current value according to the real-time current limiting state of the preceding circuit, so that the preceding circuit operates in a critical current limiting state;

[0023] When the front-stage circuit operates in a critical current limiting state, the front-stage circuit is controlled to output the AC fluctuating voltage based on the DC average voltage.

[0024] Optionally, in one embodiment of the present invention, the control unit calculates the AC fluctuating voltage using the following formula:

[0025] ;

[0026] in, is the AC fluctuating voltage, is the effective value of the voltage, is the effective value of the current, is the DC average voltage, is the angular frequency, is the capacitance, is the phase information, For time.

[0027] Optionally, in one embodiment of the present invention, the minimum value of the capacitance for:

[0028] ;

[0029] in, is the maximum average power of the inverter circuit, is the preset scale factor.

[0030] Optionally, in one embodiment of the present invention, The value range is 1.05~1.1.

[0031] The present invention proposes a power regulation system for a multi-stage inverter, which eliminates power fluctuations of the multi-stage inverter by dynamically charging and discharging by arranging a dynamic compensation capacitor between the front-stage circuit and the inverter circuit, thereby ensuring that the multi-stage inverter is in a stable operating state. In particular, a control unit connected to the front-stage circuit is also provided, which can accurately and reliably determine the AC fluctuating voltage required to be output by the front-stage circuit to match the dynamic compensation capacitor, and control the front-stage circuit to provide a suitable AC fluctuating voltage for the dynamic compensation capacitor, thereby further reducing the instantaneous power demand of the front-stage circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a circuit schematic diagram of a power regulation system for a multi-level inverter provided by one embodiment of the present invention;

[0033] Figure 2 1 is a schematic diagram of a dynamic compensation effect curve of a power regulation system of a multi-level inverter provided by an embodiment of the present invention;

[0034] Figure 3 is a circuit schematic diagram of a closed-loop control unit provided by one embodiment of the present invention;

[0035] Figure 4 1 is a schematic diagram of related current and voltage curves of a power regulation system of a multi-level inverter provided by an embodiment of the present invention, when a preset output current value is an ideal output current value;

[0036] Figure 5 This is a schematic diagram of relevant current and voltage curves of a power regulation system of a multi-level inverter provided by an embodiment of the present invention, when a preset output current value is lower than an ideal output current value;

[0037] Figure 6 This is a schematic diagram of relevant current and voltage curves of a power regulation system of a multi-level inverter provided by an embodiment of the present invention, when a preset output current value is higher than an ideal output current value;

[0038] Figure 7 It is a schematic diagram of the instantaneous waveform of the output power of the front-stage circuit provided by one embodiment of the present invention in the non-current limiting state, the intermittent current limiting state and the critical current limiting state. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] It should be noted that although the functional modules are divided in the device schematic, in some cases, the division can be performed in modules different from those in the device.

[0041] The present invention provides a power regulation system for a multi-stage inverter. The multi-stage inverter includes a front-stage circuit for outputting a DC average voltage and an inverter circuit for outputting inverter power. The power regulation system includes: a dynamic compensation capacitor connected in parallel between the front-stage circuit and the inverter circuit, for dynamically charging and discharging to eliminate power fluctuations of the multi-stage inverter, thereby reducing the instantaneous power demand of the front-stage circuit; and a control unit connected to the front-stage circuit, for determining an AC fluctuating voltage required to be output by the front-stage circuit to match the dynamic compensation capacitor, and controlling the front-stage circuit to output the AC fluctuating voltage. In the present invention, by providing a dynamic compensation capacitor between the front-stage circuit and the inverter circuit, the power fluctuations of the multi-stage inverter are eliminated by dynamic charging and discharging, ensuring that the multi-stage inverter is in a stable operating state. In particular, a control unit connected to the front-stage circuit is further provided, which can accurately and reliably determine the AC fluctuating voltage required to be output by the front-stage circuit to match the dynamic compensation capacitor, and control the front-stage circuit to provide an appropriate AC fluctuating voltage to the dynamic compensation capacitor, thereby further reducing the instantaneous power demand of the front-stage circuit.

[0042] Figure 1 A circuit schematic diagram of a power regulation system for a multi-level inverter provided by one embodiment of the present invention.

[0043] like Figure 1 As shown, the power regulation system of the multi-level inverter, wherein the multi-level inverter includes a front-stage circuit DL1 for outputting a DC average voltage and an inverter circuit DL2 for outputting an inverter power; the power regulation system specifically includes but is not limited to:

[0044] The dynamic compensation capacitor C1 is connected in parallel between the front-stage circuit DL1 and the inverter circuit DL2, and is used for dynamic charging and discharging to eliminate power fluctuations of the multi-stage inverter, thereby reducing the instantaneous power demand of the front-stage circuit DL1;

[0045] The control unit S1 is connected to the front-stage circuit DL1 and is used to determine the AC fluctuating voltage that the front-stage circuit DL1 needs to output to match the dynamic compensation capacitor C1, and control the front-stage circuit DL1 to output the AC fluctuating voltage;

[0046] The frequency of the AC fluctuating voltage is twice the frequency of the output voltage of the inverter circuit, the phase of the AC fluctuating voltage is twice the phase of the output voltage, and the amplitude of the AC fluctuating voltage can be dynamically adjusted.

[0047] Specifically, the front-stage circuit DL1 and the inverter circuit DL2 form a two-stage inverter, that is, the front-stage circuit DL1 is a DCDC circuit, and the inverter circuit DL2 is a DCAC inverter circuit. The front-stage circuit DL1 can be used to complete the boost to provide a stable DC bus voltage and achieve high-frequency isolation; since the characteristic of the inverter circuit DL2 is that the instantaneous power it outputs is a sinusoidal wave profile, the minimum value is 0 and the maximum value is 2 times the average power, the average power is the product of the output voltage effective value and the output current effective value of the inverter circuit DL2, that is, since the maximum instantaneous power of the inverter circuit DL2 can reach twice the average power, and the front-stage circuit DL1 and the inverter circuit DL2 are connected in series, then theoretically the maximum instantaneous power of the front-stage circuit DL1 also needs to reach twice the average power, so that the front-stage circuit DL1 and The instantaneous value of the power of the inverter circuit DL2 is matched, but the greater the instantaneous power, the greater the electrical stress the device will bear, the lower the reliability of the circuit will be, and the cost of selecting the device will be higher; based on this, the present application provides a power regulation system for a multi-stage inverter, which eliminates the power fluctuation of the multi-stage inverter by dynamically charging and discharging by setting a dynamic compensation capacitor C1 between the front-stage circuit DL1 and the inverter circuit DL2, ensuring that the multi-stage inverter is in a stable operating state. In particular, a control unit S1 connected to the front-stage circuit DL1 is also provided, which can accurately and reliably determine the AC fluctuating voltage required to be output by the front-stage circuit DL1 and matched with the dynamic compensation capacitor C1, and control the front-stage circuit DL1 to provide a suitable AC fluctuating voltage for the dynamic compensation capacitor C1, thereby further reducing the instantaneous power demand of the front-stage circuit DL1.

[0048] It should be noted that the specific circuit structures of the front-stage circuit DL1 and the inverter circuit DL2 belong to the relevant existing technology in this field and are well known to those skilled in the art. This part is not the main invention point of the present invention, so it will not be described in detail here. The function of the control unit S1 is to control the output voltage of the front-stage circuit DL1, so that the front-stage circuit DL1 will further superimpose the AC fluctuating voltage on the basis of the original stable DC voltage, so that the current of the front-stage circuit DL1 will be divided into two branches for transmission. The first branch is the current of the inverter circuit DL2, and the second branch is the current of the dynamic compensation capacitor C1. The control unit S1 can be set inside the front-stage circuit DL1 itself, or it can be set to be external and independent of the front-stage circuit DL1. Figure 1 In the embodiment, the control unit S1 is configured to be distinguished from the front-stage circuit DL1 , but this is not the only limitation.

[0049] In one embodiment, the control unit may, but is not limited to, determine the AC fluctuating voltage required to be output by the pre-stage circuit and matched to the dynamic compensation capacitor in the following manner:

[0050] Obtaining an output voltage waveform of the inverter circuit, and determining voltage RMS, angular frequency, and phase information of the inverter circuit based on the output voltage waveform;

[0051] Obtaining an output current waveform of the inverter circuit, and determining an effective current value of the inverter circuit according to the output current waveform;

[0052] Obtain the DC average voltage output by the previous stage circuit and the capacitance of the dynamic compensation capacitor;

[0053] According to the voltage effective value, angular frequency, phase information, current effective value, DC average voltage and capacitance, the AC fluctuating voltage required to be output by the front-stage circuit to match the dynamic compensation capacitor is determined.

[0054] Specifically, on the one hand, considering the influence of the output current, that is, under the same voltage fluctuation, the larger the capacitance of the dynamic compensation capacitor, the larger the current flowing through the dynamic compensation capacitor, and conversely, the smaller the capacitance of the dynamic compensation capacitor, the smaller the current flowing through the dynamic compensation capacitor. Therefore, the capacitance of the dynamic compensation capacitor and the magnitude of the voltage fluctuation will affect the magnitude of the current flowing through the dynamic compensation capacitor, thereby affecting the current of the previous stage circuit; on the other hand, considering the phase of the dynamic compensation capacitor current, the current phase of the dynamic compensation capacitor leads the voltage phase by 90°. If the current direction of the dynamic compensation capacitor and the current direction of the inverter circuit are both positive, the current superposition of the previous stage circuit is greater. If the current direction of the dynamic compensation capacitor and the current direction of the inverter circuit are opposite, the current cancellation of the previous stage circuit becomes smaller. It can be seen that the current size and phase of the dynamic compensation capacitor determine whether the current of the previous stage circuit is more or less superimposed or cancelled. For example, the control unit can, but is not limited to, use the following formula to calculate the AC fluctuating voltage:

[0055] ;

[0056] in, is the AC fluctuating voltage, is the effective value of voltage, is the effective value of current, is the average DC voltage, is the angular frequency, is the capacitance, is the phase information, For time.

[0057] Reference Figure 2, I1 is the current waveform input to the inverter circuit without any compensation, I2 is the desired current waveform of the branch corresponding to the dynamic compensation capacitor, which is used to offset the input current of the inverter circuit, I3 is the output current waveform of the previous stage circuit after the current of the branch corresponding to the dynamic compensation capacitor is offset, and V1 is the AC waveform of the dynamic compensation capacitor voltage when it is powered on, which is obtained by inverting the current waveform of the dynamic compensation capacitor. It can be seen that the AC voltage satisfies the above calculation formula, which is also an important basis for deriving the calculation formula.

[0058] In one embodiment, the control unit may, but is not limited to, specifically control the front-stage circuit to output the AC fluctuating voltage in the following manner:

[0059] The current stage circuit uses an output programmable circuit to inject an AC fluctuation waveform on the basis of the DC average voltage. The frequency of the AC fluctuation waveform is twice the frequency of the output voltage waveform, the phase of the AC fluctuation waveform is twice the phase of the output voltage waveform, and the amplitude of the AC fluctuation waveform can be dynamically adjusted.

[0060] Reading the output current fluctuation amplitude of the preceding circuit and continuously controlling the output current fluctuation amplitude until a target current fluctuation condition is met, wherein the target current fluctuation condition is that the output current fluctuation amplitude is less than or equal to a preset current fluctuation amplitude;

[0061] The output of the AC fluctuation waveform that meets the target current fluctuation condition is used as the AC fluctuation voltage, and the front-stage circuit is controlled to output the AC fluctuation voltage based on the DC average voltage.

[0062] It should be noted that the preset current fluctuation amplitude can be set accordingly according to the specific application scenario, and there is no restriction here; the specific process of continuously controlling the output current fluctuation amplitude is determined according to different scenarios, for example, comparison is made according to different reading times. When the difference between the output current amplitude read last time and the output current amplitude read next time (that is, the output current fluctuation amplitude) is judged to be less than or equal to the preset current fluctuation amplitude, then there is no need to continue sampling and reading, and the target current fluctuation condition has been met. Otherwise, continuous sampling, reading and control are required until the target current fluctuation condition is met.

[0063] In one embodiment, the control unit may, but is not limited to, specifically control the output of the AC fluctuating voltage by the front-stage circuit in the following manner:

[0064] When the current stage circuit adopts an output voltage closed-loop control circuit, and the previous stage circuit includes a closed-loop control unit, the instantaneous value of the AC voltage of the previous stage circuit is superimposed on the AC fluctuating voltage given by the control unit, thereby controlling the closed-loop control unit to keep the instantaneous value of the AC voltage consistent with the AC fluctuating voltage based on the PID algorithm;

[0065] The front-stage circuit is controlled to output an AC fluctuating voltage based on the DC average voltage.

[0066] Reference Figure 3 , the instantaneous value of the output voltage of the AC fluctuation waveform is superimposed on the output voltage value given by the control unit, and the output of the previous stage circuit is controlled by the closed-loop control unit of the previous stage circuit to be consistent with the output voltage value given by the control unit, that is, the target current fluctuation condition can be met; specifically, the basic working principle of the closed-loop control unit is: through negative feedback regulation, the controlled object is kept close to the given target in real time, that is, the goal is to change the output voltage of the previous stage circuit from the original DC average voltage Instead, superimpose AC fluctuating voltage on the fixed voltage , AC fluctuating voltage The frequency is twice the output voltage frequency of the inverter circuit, and the AC fluctuating voltage The phase follows twice the voltage phase of the inverter circuit, and the AC fluctuating voltage The magnitude of depends on the DC average voltage and the capacitance of the dynamic compensation capacitor, which is controlled by the PID controller (i.e. Figure 3 "PI" shown in ) combined with proportional gain A closed-loop regulation function is achieved so that the output of the previous stage circuit remains the same as the target setting, so that the error is close to 0, thus achieving the purpose of the previous stage circuit outputting DC superimposed on a specific AC.

[0067] In one embodiment, the control unit may, but is not limited to, specifically control the output of the AC fluctuating voltage by the front-stage circuit in the following manner:

[0068] When the current stage circuit adopts a constant voltage and current limiting output function circuit, the control unit obtains the output current of the previous stage circuit, and if the output current of the current stage circuit is greater than the preset output current value, the previous stage circuit is controlled to output at the preset output current value, otherwise the previous stage circuit is controlled to output at a constant voltage;

[0069] Reading the real-time current limiting state of the preceding circuit, and adaptively adjusting the preset output current value according to the real-time current limiting state of the preceding circuit, so that the preceding circuit operates in a critical current limiting state;

[0070] When the front-stage circuit operates in a critical current limiting state, the front-stage circuit is controlled to output an AC fluctuating voltage based on a DC average voltage.

[0071] Specifically, based on the principle of dynamic capacitor compensation, under ideal conditions with good compensation, the output current of the front-stage circuit is a nearly steady current, and its current limit is close to the average power required by the inverter circuit. Ideally, the AC component of the front-stage circuit's output is completely absorbed by the dynamic compensation capacitor, and the front-stage circuit can be considered to output only the DC component. This means that the front-stage circuit reaches a critical current limiting state. That is, the critical current limiting state means that if the preset output current value is adjusted further in the direction of increasing, there will be no current limiting, while if it is adjusted further in the direction of decreasing, there will be continuous current limiting. In other words, the ideal state of critical current limiting is that within an adjustment cycle, the current is limited in the previous cycle and not limited in the next cycle, and the interval adjustment cycle is one of two different states: current limited and not limited. Therefore, in order to make the front-stage circuit reach the critical current limiting state, the control unit needs to read the real-time current limiting state of the front-stage circuit and perform auxiliary adjustment by adjusting the preset output current value in real time. When it is read that the front-stage circuit is in the current limiting state, the preset output current value is adjusted upward until the current limiting state of the front-stage circuit disappears; when the actual output current value of the front-stage circuit is less than the preset output current value, the preset output current value is adjusted downward until the front-stage circuit enters the current limiting state; it can be seen that the preset output current value is adaptively adjusted based on the real-time current limiting state of the front-stage circuit, so that the preset output current value is adjusted to the ideal output current value, so that the front-stage circuit is always in the critical current limiting state, thereby avoiding the front-stage circuit from continuously operating in the current limiting state or continuously operating in the non-current limiting state.

[0072] like Figure 4 As shown, the preset output current value corresponds to the ideal output current value. At this time, the front-stage circuit is in a critical current limiting state, wherein I31 is the output current of the front-stage circuit in the critical current limiting state, I32 is the input current of the inverter circuit, V31 is the voltage across the dynamic compensation capacitor, and I33 is the current flowing through the dynamic compensation capacitor.

[0073] like Figure 5 As shown, corresponding to the case where the preset output current value is lower than the ideal output current value, I34 is the output current of the front-stage circuit. In each adjustment cycle, the front-stage circuit operates in the current-limited output state, and its output current remains stable; I35 is the input current of the inverter circuit, I36 is the current flowing through the dynamic compensation capacitor, and V32 is the voltage across the dynamic compensation capacitor. Since the current-limited output power does not meet the average power requirement of the inverter circuit, Figure 4 It can be seen that V32 as the DC average voltage will continue to decrease, causing the DC average voltage to fail to meet the input voltage conditions of the inverter circuit, which in turn causes the multi-level inverter to be unable to perform dynamic compensation and work normally.

[0074] like Figure 6As shown, corresponding to the case where the preset output current value is higher than the ideal output current value, I37 is the output current of the front-stage circuit, I38 ​​is the input current of the inverter circuit, I39 is the current flowing through the dynamic compensation capacitor, and V33 is the voltage across the dynamic compensation capacitor; at this time, an unlimited current state occurs locally, and when the preset output current value is further increased, the local unlimited current state will occupy more cycles. The extreme state is that no current limiting occurs in all working cycles. When the front-stage circuit is completely unlimited, it works in a constant voltage output mode. Since there is no AC fluctuating voltage on the dynamic compensation capacitor, no current will flow through. The output voltage of the front-stage circuit will also fluctuate at twice the frequency, which will generate a counteracting current on the dynamic compensation capacitor. The purpose of reducing the peak power of the front-stage circuit can also be achieved. In other words, the power of the front-stage circuit will fluctuate with the current limiting state and the unlimited current state, but the maximum power is still relatively reduced compared to when there is no dynamic compensation capacitor compensation. Therefore, even if the control unit cannot completely make the previous stage circuit operate in the critical current limiting state, local current limiting can still achieve the effect of dynamic compensation of the capacitor. It’s just that the compensation effect is optimal in the critical current limiting state, which is not limited here. In other words, local current limiting greatly reduces the control requirements of the control unit for the previous stage circuit, and can balance the performance of the control unit with the optimal compensation effect.

[0075] In summary, if the preset output current value is always too low, the DC average voltage will continue to decrease, which will not meet the input voltage requirements of the multi-stage inverter. If the preset output current value is always too high, the front-stage circuit will continue to be in an unlimited current state, causing the front-stage circuit to work in a constant voltage output state, and there will be no compensation current on the dynamic compensation capacitor. By adjusting the preset output current value corresponding to the front-stage circuit, the front-stage circuit can be made to work between the above two states, with critical current limiting or intermittent current limiting, so that the desired fluctuating voltage can appear on the dynamic compensation capacitor. Figure 7As shown in the figure, from top to bottom are the instantaneous waveforms of the output power of the front-stage circuit in the unlimited current state, intermittent current limiting state and critical current limiting state. In the case of unlimited current, it is equivalent to not adding dynamic compensation, the instantaneous power maximum value is 40KW, the minimum value is 0KW, and the average power is 20KW; in the intermittent current limiting state, there is capacitor dynamic compensation, the instantaneous power maximum value is 22KW, the minimum value is 14KW, and the average power is 20KW; in the critical current limiting state, there is capacitor dynamic compensation, the instantaneous power maximum value is 20.4KW, the minimum value is 18.7KW, and the average power is 20KW. It can be seen that in the critical current limiting state, the capacitor dynamic compensation effect is relatively the best. For an inverter with an average power of 20KW, the peak power is 40KW, and the maximum power of the front-stage circuit only needs 20.4KW, and does not need to be set to 40KW. Obviously, this greatly reduces the peak power demand for the front-stage circuit, thereby reducing the design cost of the front-stage circuit and improving the reliability of the overall operation of the front-stage circuit and the inverter.

[0076] In one embodiment, the minimum capacitance of the dynamic compensation capacitor is for:

[0077] ;

[0078] in, is the maximum average power of the inverter circuit, is the preset scale factor.

[0079] Specifically, it is known in the aforementioned embodiments that ,when , Take it as the minimum value, then the voltage across the dynamic compensation capacitor is , this voltage should not be lower than the minimum input voltage of the inverter circuit, and the minimum input voltage of the inverter circuit is ,in is a preconfigured scaling factor that takes into account the actual line voltage drop and inverter modulation ratio. It can be, but is not limited to, 1.05~1.1. The capacitance of the dynamic compensation capacitor in the corresponding case should not be less than Furthermore, considering that the output power of the inverter circuit will change with the load, and the dynamic compensation capacitor in the actual application scenario will be selected in advance and will not change with the load change, the dynamic compensation capacitor should be selected according to the maximum average power of the inverter circuit as much as possible, that is, the above formula provides .

[0080] It should be noted that the power regulation system and application scenario of the multi-stage inverter described in the embodiment of the present invention are intended to more clearly illustrate the technical solution of the embodiment of the present invention, and do not constitute a limitation on the technical solution provided by the embodiment of the present invention. Those skilled in the art will know that with the evolution of the power regulation system of the multi-stage inverter and the emergence of new application scenarios, the technical solution provided by the embodiment of the present invention is also applicable to similar technical problems.

[0081] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A power regulation system for a multi-level inverter, characterized in that: The multi-stage inverter includes a front-stage circuit for outputting a DC average voltage and an inverter circuit for outputting an inverter power. The power regulation system includes: a dynamic compensation capacitor connected in parallel between the front-stage circuit and the inverter circuit, for dynamically charging and discharging to eliminate power fluctuations of the multi-stage inverter, thereby reducing the instantaneous power demand of the front-stage circuit; a control unit, connected to the front-stage circuit and the inverter circuit, respectively, for determining the AC fluctuating voltage required to be output by the front-stage circuit and matching the dynamic compensation capacitor, and controlling the front-stage circuit to output the AC fluctuating voltage; The frequency of the AC fluctuating voltage is twice the frequency of the output voltage of the inverter circuit, the phase of the AC fluctuating voltage is twice the phase of the output voltage, and the amplitude of the AC fluctuating voltage can be dynamically adjusted. The control unit specifically determines the AC fluctuating voltage required to be output by the front-stage circuit and matched with the dynamic compensation capacitor in the following manner: Acquiring an output voltage waveform of the inverter circuit, and determining a voltage effective value, an angular frequency, and phase information of the inverter circuit according to the output voltage waveform; Acquiring an output current waveform of the inverter circuit, and determining an effective current value of the inverter circuit according to the output current waveform; Obtaining the average DC voltage output by the preceding circuit and the capacitance of the dynamic compensation capacitor; The AC fluctuating voltage required to be output by the front-stage circuit and matching the dynamic compensation capacitor is determined according to the voltage effective value, the angular frequency, the phase information, the current effective value, the DC average voltage and the capacitance.

2. The power regulation system of the multi-level inverter according to claim 1, characterized in that: The control unit specifically controls the front-stage circuit to output the AC fluctuating voltage in the following manner: When the front-stage circuit adopts an output programmable circuit, an AC fluctuating waveform is injected into the DC average voltage, wherein the frequency of the AC fluctuating waveform is twice the frequency of the output voltage waveform, the phase of the AC fluctuating waveform is twice the phase of the output voltage waveform, and the amplitude of the AC fluctuating waveform can be dynamically adjusted; reading an output current fluctuation amplitude of the preceding circuit, and continuously controlling the output current fluctuation amplitude until a target current fluctuation condition is met, wherein the target current fluctuation condition is that the output current fluctuation amplitude is less than or equal to a preset current fluctuation amplitude; The AC ripple waveform that satisfies the target current ripple condition is output as the AC ripple voltage, and the front-stage circuit is controlled to output the AC ripple voltage based on the DC average voltage.

3. The power regulation system of the multi-level inverter according to claim 1, characterized in that: The control unit specifically controls the front-stage circuit to output the AC fluctuating voltage in the following manner: When the front-stage circuit adopts an output voltage closed-loop control circuit and the front-stage circuit includes a closed-loop control unit, the instantaneous value of the AC voltage of the front-stage circuit is superimposed on the AC fluctuating voltage given by the control unit, thereby controlling the closed-loop control unit to keep the instantaneous value of the AC voltage consistent with the AC fluctuating voltage based on a PID algorithm; The front-stage circuit is controlled to output the AC fluctuating voltage based on the DC average voltage.

4. The power regulation system of the multi-level inverter according to claim 1, characterized in that: The control unit specifically controls the front-stage circuit to output the AC fluctuating voltage in the following manner: When the front-stage circuit adopts a constant voltage and current limiting output function circuit, the control unit obtains the output current of the front-stage circuit, and when the output current of the front-stage circuit is greater than a preset output current value, controls the front-stage circuit to output at the preset output current value; otherwise, controls the front-stage circuit to output at a constant voltage; reading a real-time current limiting state of the preceding circuit, and adaptively adjusting the preset output current value according to the real-time current limiting state of the preceding circuit, so that the preceding circuit operates in a critical current limiting state; When the front-stage circuit operates in a critical current limiting state, the front-stage circuit is controlled to output the AC fluctuating voltage based on the DC average voltage.

5. The power regulation system of the multi-level inverter according to claim 1, characterized in that: The control unit calculates the AC fluctuating voltage using the following formula: Among them, V ac is the AC fluctuating voltage, V is the effective value of the voltage, I is the effective value of the current, V dc is the DC average voltage, ω is the angular frequency, C is the capacitance, ωt is the phase information, and t is time.

6. The power regulation system of the multi-level inverter according to claim 5, characterized in that: The minimum value of the capacitance C min for: Among them, P max is the maximum average power of the inverter circuit, and m is a preset proportional coefficient.

7. The power regulation system of the multi-level inverter according to claim 6, characterized in that: The value range of m is 1.05~1.1.

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