Power regulation system of multi-stage inverter

Abstract

The invention relates to the technical field of power electronic control, and particularly discloses a power regulation system of a multi-stage inverter, which is characterized in that a dynamic compensation capacitor is arranged between a pre-stage circuit and an inverter circuit to dynamically charge and discharge to eliminate power fluctuation of the multi-stage inverter and ensure that the multi-stage inverter is in a stable operation working state, and particularly, the power regulation system of the multi-stage inverter can regulate the power fluctuation of the multi-stage inverter. In addition, a control unit connected to the pre-stage circuit is arranged, the alternating current fluctuation voltage which needs to be output by the pre-stage circuit and is matched with the dynamic compensation capacitor can be accurately and reliably determined, the pre-stage circuit is controlled to provide the appropriate alternating current fluctuation voltage for the dynamic compensation capacitor, and therefore the instantaneous power requirement of the pre-stage circuit can be further lowered.

Description

Technical Field

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

[0002] With the continuous development of the power electronics industry, multilevel inverters are increasingly widely used. Generally speaking, a multilevel inverter can be divided into a front-stage DCDC circuit and a rear-stage DCAC inverter circuit; in a multilevel inverter, 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 components in the front-stage circuit and relatively high costs. At present, related technologies improve this situation by adding an LC filter circuit between the front and rear-stage circuits. Although it can partially smooth the current, since the inverter usually operates at power frequency, in the LC filter circuit, the filter inductor and capacitor are large in volume and there is a risk of resonance, which easily leads to voltage out-of-control between the front and rear-stage circuits, causing power fluctuations in the multilevel inverter. Summary of the Invention

[0003] The present invention aims to at least partly solve one of the technical problems in the related technologies. For this purpose, the present invention provides a power regulation system for a multilevel inverter, which can eliminate the power fluctuations of the multilevel inverter.

[0004] In a first aspect, an embodiment of the present invention provides a power regulation system for a multilevel inverter. The multilevel 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 the power fluctuations of the multilevel inverter, so as to reduce the instantaneous power demand of the front-stage circuit; A control unit, respectively connected to the front-stage circuit and the inverter circuit, for determining an AC fluctuation voltage output by the front-stage circuit that matches the dynamic compensation capacitor, and controlling the front-stage circuit to output the AC fluctuation voltage; Wherein, the frequency of the AC fluctuation voltage is twice the frequency of the output voltage of the inverter circuit, the phase of the AC fluctuation voltage is twice the phase of the output voltage, and the amplitude of the AC fluctuation voltage can be dynamically adjusted.

[0005] Optionally, in an embodiment of the present invention, the control unit specifically determines the AC fluctuation voltage output by the front-stage circuit that matches the dynamic compensation capacitor in the following manner: Obtain the output voltage waveform of the inverter circuit, and determine the voltage effective value, angular frequency and phase information of the inverter circuit according to the output voltage waveform; Obtain the output current waveform of the inverter circuit, and determine the effective value of the current of the inverter circuit according to the output current waveform; Obtain the DC average voltage output by the front-stage circuit and the capacitance of the dynamic compensation capacitor; According to the voltage effective value, the angular frequency, the phase information, the current effective value, the DC average voltage and the capacitance, determine the AC fluctuation voltage that needs to be output by the front-stage circuit and matches the dynamic compensation capacitor.

[0006] Optionally, in an embodiment of the present invention, the control unit specifically controls the front-stage circuit to output the AC fluctuation voltage in the following manner: When the front-stage circuit adopts an output programmable circuit, an AC fluctuation waveform is injected on the basis of the DC average voltage, where 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; Read the output current fluctuation amplitude of the front-stage circuit, and continuously control the output current fluctuation amplitude until the target current fluctuation condition is met, where the target current fluctuation condition is that the output current fluctuation amplitude is less than or equal to the preset current fluctuation amplitude; Use the output of the AC fluctuation waveform that meets the target current fluctuation condition as the AC fluctuation voltage, and control the front-stage circuit to output the AC fluctuation voltage on the basis of the DC average voltage.

[0007] Optionally, in an embodiment of the present invention, the control unit specifically controls the front-stage circuit to output the AC fluctuation 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, superimpose the instantaneous value of the AC voltage of the front-stage circuit on the AC fluctuation voltage given by the control unit, so as to control the closed-loop control unit to keep the instantaneous value of the AC voltage consistent with the AC fluctuation voltage based on the PID algorithm; Control the front-stage circuit to output the AC fluctuation voltage on the basis of the DC average voltage.

[0008] Optionally, in an embodiment of the present invention, the control unit specifically controls the front-stage circuit to output the AC fluctuation voltage in the following manner: When the pre-stage circuit adopts a constant-voltage and current-limiting output functional circuit, the control unit acquires the output current of the pre-stage circuit, and when the output current of the pre-stage circuit is greater than a preset output current value, controls the pre-stage circuit to output at the preset output current value; otherwise, controls the pre-stage circuit to perform constant-voltage output; Reads the real-time current-limiting state of the pre-stage circuit, and adaptively adjusts the preset output current value according to the real-time current-limiting state of the pre-stage circuit, so that the pre-stage circuit operates in a critical current-limiting state; When the pre-stage circuit operates in a critical current-limiting state, controls the pre-stage circuit to output the AC fluctuation voltage based on the DC average voltage.

[0009] Optionally, in an embodiment of the present invention, the control unit calculates the AC fluctuation voltage using the following formula: ; Wherein, is the AC fluctuation voltage, is the effective voltage value, is the effective current value, is the DC average voltage, is the angular frequency, is the capacitance, is the phase information, is the time.

[0010] Optionally, in an embodiment of the present invention, the minimum value of the capacitance is: ; Wherein, is the maximum average power of the inverter circuit, is a preset proportionality coefficient.

[0011] Optionally, in an embodiment of the present invention, the value range of is 1.05 to 1.1.

[0012] A power regulation system for a multi-level inverter proposed by the present invention sets a dynamic compensation capacitor between the pre-stage circuit and the inverter circuit to eliminate the power fluctuation of the multi-level inverter through dynamic charging and discharging, ensuring that the multi-level inverter is in a stable operating state. In particular, a control unit connected to the pre-stage circuit is also provided, which can accurately and reliably determine the AC fluctuation voltage required for the pre-stage circuit to match the dynamic compensation capacitor, and control the pre-stage circuit to provide a suitable AC fluctuation voltage for the dynamic compensation capacitor, thereby further reducing the instantaneous power demand of the pre-stage circuit. Description of the Drawings

[0013] Figure 1 It is the circuit schematic diagram of the power regulation system of the multi-level inverter provided by an embodiment of the present invention; Figure 2 It is the schematic diagram of the dynamic compensation effect curve of the power regulation system of the multi-level inverter provided by an embodiment of the present invention; Figure 3 It is the circuit schematic diagram of the closed-loop control unit provided by an embodiment of the present invention; Figure 4 It is the schematic diagram of the curves of relevant currents and voltages of the power regulation system of the multi-level inverter provided by an embodiment of the present invention when the preset output current value is the ideal output current value; Figure 5 It is the schematic diagram of the curves of relevant currents and voltages of the power regulation system of the multi-level inverter provided by an embodiment of the present invention when the preset output current value is lower than the ideal output current value; Figure 6 It is the schematic diagram of the curves of relevant currents and voltages of the power regulation system of the multi-level inverter provided by an embodiment of the present invention when the preset output current value is higher than the ideal output current value; Figure 7 It is the schematic diagram of the instantaneous waveform of the output power of the pre-stage circuit in the non-current-limiting state, intermittent current-limiting state, and critical current-limiting state provided by an embodiment of the present invention. Detailed implementation manners

[0014] In order to make the objectives, technical solutions and advantages of the present invention clearer, 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 used to limit the present invention.

[0015] It should be noted that although the functional modules are divided in the device schematic diagram, in some cases, they can be divided differently from the modules in the device.

[0016] The present invention provides a power regulation system for a multi-level inverter. The multi-level inverter includes a pre-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 pre-stage circuit and the inverter circuit, for dynamically charging and discharging to eliminate the power fluctuation of the multi-level inverter, so as to reduce the instantaneous power demand of the pre-stage circuit; a control unit, connected to the pre-stage circuit, for determining the AC fluctuation voltage matching the dynamic compensation capacitor required to be output by the pre-stage circuit, and controlling the pre-stage circuit to output the AC fluctuation voltage. In the present invention, by arranging a dynamic compensation capacitor between the pre-stage circuit and the inverter circuit, the power fluctuation of the multi-level inverter is eliminated by dynamic charging and discharging, ensuring that the multi-level inverter is in a stable operating state. In particular, a control unit connected to the pre-stage circuit is also provided, which can accurately and reliably determine the AC fluctuation voltage matching the dynamic compensation capacitor required to be output by the pre-stage circuit, and control the pre-stage circuit to provide a suitable AC fluctuation voltage for the dynamic compensation capacitor, thereby further reducing the instantaneous power demand of the pre-stage circuit.

[0017] Figure 1 It is a circuit schematic diagram of a power regulation system for a multi-level inverter provided by an embodiment of the present invention.

[0018] As Figure 1 shown, for the power regulation system of the multi-level inverter, wherein, the multi-level inverter includes a pre-stage circuit DL1 for outputting a DC average voltage and an inverter circuit DL2 for outputting inverter power; the power regulation system specifically includes but is not limited to: A dynamic compensation capacitor C1, connected in parallel between the pre-stage circuit DL1 and the inverter circuit DL2, for dynamically charging and discharging to eliminate the power fluctuation of the multi-level inverter, so as to reduce the instantaneous power demand of the pre-stage circuit DL1; A control unit S1, connected to the pre-stage circuit DL1, for determining the AC fluctuation voltage matching the dynamic compensation capacitor C1 required to be output by the pre-stage circuit DL1, and controlling the pre-stage circuit DL1 to output the AC fluctuation voltage; Wherein, the frequency of the AC fluctuation voltage is twice the frequency of the output voltage of the inverter circuit, the phase of the AC fluctuation voltage is twice the phase of the output voltage, and the amplitude of the AC fluctuation voltage can be dynamically adjusted.

[0019] Specifically, the pre-stage circuit DL1 and the inverter circuit DL2 form a two-stage inverter. That is, the pre-stage circuit DL1 is a DCDC circuit, and the inverter circuit DL2 is a DCAC inverter circuit. The pre-stage circuit DL1 can be used to complete voltage boosting 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 output by it is a sine wave profile, the minimum value is 0, and the maximum value is twice the average power. This average power is the product of the effective value of the output voltage and the effective value of the output current of the inverter circuit DL2. That is to say, since the maximum instantaneous power of the inverter circuit DL2 can reach twice the average power, and the pre-stage circuit DL1 and the inverter circuit DL2 are connected in series, then theoretically, the maximum instantaneous power of the pre-stage circuit DL1 also needs to reach twice the average power in order to make the instantaneous power values of the pre-stage circuit DL1 and the inverter circuit DL2 match. However, the greater the instantaneous power, the greater the electrical stress borne by the device, the lower the reliability of the circuit, and the higher the cost of the selected device. Based on this, a power regulation system for a multi-stage inverter provided in this application sets a dynamic compensation capacitor C1 between the pre-stage circuit DL1 and the inverter circuit DL2 to eliminate the power fluctuation of the multi-stage inverter through dynamic charging and discharging, ensuring that the multi-stage inverter is in a stable operating state. In particular, a control unit S1 connected to the pre-stage circuit DL1 is also provided, which can accurately and reliably determine the AC fluctuation voltage required for the pre-stage circuit DL1 to match the dynamic compensation capacitor C1, and control the pre-stage circuit DL1 to provide a suitable AC fluctuation voltage for the dynamic compensation capacitor C1, thereby further reducing the instantaneous power requirement of the pre-stage circuit DL1.

[0020] It should be noted that the specific circuit structures of the pre-stage circuit DL1 and the inverter circuit DL2 belong to the related prior art in this field and are well-known to those skilled in the art. And this part is not the main inventive point of the present invention, so it will not be elaborated here. The function of the control unit S1 is to control the output voltage of the pre-stage circuit DL1, so that the pre-stage circuit DL1 will further superimpose an AC fluctuation voltage on the original stable DC voltage. In this way, the current of the pre-stage circuit DL1 will be transmitted in two branches. The first branch is the current of the inverter circuit DL2, and the second branch is the current of the dynamic compensation capacitor C1. Among them, the control unit S1 can be set inside the pre-stage circuit DL1 itself or set as an external unit independent of the pre-stage circuit DL1. Figure 1 In [the reference], the control unit S1 and the pre-stage circuit DL1 are set separately, but this is not the only limitation.

[0021] In one embodiment, the control unit can, but is not limited to, determine the AC fluctuation voltage required for the pre-stage circuit to match the dynamic compensation capacitor through the following methods: Obtain the output voltage waveform of the inverter circuit, and determine the effective value of the voltage, angular frequency, and phase information of the inverter circuit according to the output voltage waveform; Obtain the output current waveform of the inverter circuit, and determine the effective value of the current of the inverter circuit according to the output current waveform; Obtain the DC average voltage output by the pre-stage circuit and the capacitance of the dynamic compensation capacitor; According to the effective value of the voltage, angular frequency, phase information, effective value of the current, DC average voltage, and capacitance, determine the AC fluctuating voltage that the pre-stage circuit needs to output and matches the dynamic compensation capacitor.

[0022] Specifically, on the one hand, considering the influence of the magnitude 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. On the contrary, 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 pre-stage circuit. On the other hand, considering the phase of the current of the dynamic compensation capacitor, the current phase of the dynamic compensation capacitor leads the voltage phase by 90°. If the current directions of the dynamic compensation capacitor and the inverter circuit are both positive, the current of the pre-stage circuit will be superimposed more. If the current directions of the dynamic compensation capacitor and the inverter circuit are opposite, the current of the pre-stage circuit will be cancelled less. Thus, it can be seen that the magnitude and phase of the current of the dynamic compensation capacitor determine whether the current of the pre-stage circuit is superimposed more or cancelled more. For example, the control unit can but is not limited to use the following formula to calculate the AC fluctuating voltage: ; Among them, 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, is the time.

[0023] Refer to Figure 2 , I1 is the current waveform input by the inverter circuit without any compensation, I2 is the current waveform of the corresponding branch of the desired dynamic compensation capacitor, which is used to cancel the input current of the inverter circuit, I3 is the output current waveform of the pre-stage circuit after the current of the corresponding branch of the dynamic compensation capacitor is cancelled, and V1 is the AC waveform on the power supply of the dynamic compensation capacitor inversely deduced according to the current waveform of the dynamic compensation capacitor. It can be seen that this AC voltage satisfies the above calculation formula, which is also an important basis for deriving this calculation formula.

[0024] In one embodiment, the control unit can, but is not limited to, specifically control the front-stage circuit to output an AC fluctuating voltage in the following manner: When the front-stage circuit adopts an output programmable circuit, an AC fluctuating waveform is injected on the basis of the DC average voltage. Among them, 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; Read the amplitude of the output current fluctuation of the front-stage circuit, and continuously control the amplitude of the output current fluctuation until the target current fluctuation condition is met. Among them, the target current fluctuation condition is that the amplitude of the output current fluctuation is less than or equal to the preset current fluctuation amplitude; Use the output of the AC fluctuating waveform that meets the target current fluctuation condition as the AC fluctuating voltage, and control the front-stage circuit to output the AC fluctuating voltage on the basis of the DC average voltage.

[0025] It should be noted that the preset current fluctuation amplitude can be set accordingly according to the specific application scenario, and there is no limitation here; the specific process of continuously controlling the amplitude of the output current fluctuation is determined according to different scenarios. For example, it is compared according to different reading times. When the difference between the output current amplitude read last time and the output current amplitude read next time (i.e., the amplitude of the output current fluctuation) is judged to be less than or equal to the preset current fluctuation amplitude, then there is no need to continue sampling and reading. At this time, the target current fluctuation condition has been met. Otherwise, it is necessary to continuously sample and read and control until the target current fluctuation condition is met.

[0026] In one embodiment, the control unit can, but is not limited to, specifically control the front-stage circuit to output an 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, so as to control 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; Control the front-stage circuit to output an AC fluctuating voltage on the basis of the DC average voltage.

[0027] Refer to Figure 3 , superimpose the instantaneous value of the output voltage of the AC fluctuating waveform on the output voltage value given by the control unit, and control the output of the front-stage circuit to be consistent with the output voltage value given by the control unit through the closed-loop control unit of the front-stage circuit, 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 target is to change the output voltage of the front-stage circuit, from the original DC average voltage Change to superimpose an AC fluctuating voltage on the basis of a fixed voltage , the AC fluctuating voltage has a frequency that is twice the output voltage frequency of the inverter circuit. The AC fluctuating voltage has a phase that follows twice the voltage phase of the inverter circuit. The amplitude of the AC fluctuating voltage depends on the DC average voltage and the capacitance of the dynamic compensation capacitor. Through the PID controller (i.e., Figure 3 "PI" shown in ), the closed-loop regulation effect is achieved by combining the proportional gain

[0028] so that the output of the pre-stage circuit remains the same as the target setting, and the error is close to 0, thus achieving the purpose of outputting DC superimposed with a specific AC in the pre-stage circuit. In one embodiment, the control unit can, but is not limited to, specifically control the output of the AC fluctuating voltage of the pre-stage circuit in the following manner: When the pre-stage circuit adopts a constant voltage and current limiting output functional circuit, the control unit obtains the output current of the pre-stage circuit. And when the output current of the pre-stage circuit is greater than the preset output current value, control the pre-stage circuit to output at the preset output current value; otherwise, control the pre-stage circuit to output at a constant voltage; Read the real-time current limiting state of the pre-stage circuit, and adaptively adjust the preset output current value according to the real-time current limiting state of the pre-stage circuit so that the pre-stage circuit operates in a critical current limiting state;

[0029] Specifically, according to the principle of capacitive dynamic compensation, in the ideal state of good compensation, the output current of the pre-stage circuit is a current that is close to being stable, and its current limiting value is close to the average power required by the inverter circuit. In the ideal state, all the AC components in the output part of the pre-stage circuit are absorbed by the dynamic compensation capacitor, and it can be considered that the pre-stage circuit only outputs DC components, so the pre-stage circuit reaches the critical current limiting state. That is to say, the critical current limiting state means that if the preset output current value is adjusted in the larger direction, there will be no current limiting, and if it is adjusted in the smaller direction, there will be continuous current limiting. That is, the ideal state of critical current limiting is that within the adjustment period, the previous period is current limited, and the next period is not current limited, and within the interval adjustment periods, there are two different states of current limiting and not current limiting respectively. Therefore, in order to make the pre-stage circuit reach the critical current limiting state, the control unit needs to read the real-time current limiting state of the pre-stage circuit and perform auxiliary adjustment by adjusting the preset output current value in real time. When it reads that the pre-stage circuit is in the current limiting state, it increases the preset output current value until the current limiting state of the pre-stage circuit disappears; when the actual output current value of the pre-stage circuit is less than the preset output current value, it decreases the preset output current value until the pre-stage circuit shows 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 pre-stage circuit, so as to adjust the preset output current value to the ideal output current value, making the pre-stage circuit always in the critical current limiting state, thus avoiding the pre-stage circuit from continuously working in the current limiting state or continuously working in the non-current limiting state.

[0030] As Figure 4 shown, corresponding to the case where the preset output current value is the ideal output current value, at this time the pre-stage circuit is in the critical current limiting state, where I31 is the output current of the pre-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.

[0031] As Figure 5 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 pre-stage circuit. In each adjustment period, the pre-stage circuit works in the current limiting 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, V32 is the voltage across the dynamic compensation capacitor. Since the current limiting output power does not meet the average power requirement of the inverter circuit, as Figure 4 can be seen from it, V32, as the DC average voltage, will continue to drop, resulting in the DC average voltage not meeting the input voltage condition of the inverter circuit, and further causing the multi-stage inverter to be unable to perform dynamic compensation and work properly.

[0032] As 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 pre-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, a non-current-limiting state appears locally. When the preset output current value is further increased, the non-current-limiting state will occupy more cycles locally. The extreme state is that there is no current limiting in all working cycles. When the pre-stage circuit is completely non-current-limiting, it operates in a constant voltage output mode. Since there is no AC fluctuating voltage on the dynamic compensation capacitor, no current will pass through it. The output voltage of the pre-stage circuit will also have a double-frequency fluctuation, which will generate a canceling current on the dynamic compensation capacitor, and the purpose of reducing the peak power of the pre-stage circuit can also be achieved. That is to say, the power of the pre-stage circuit will fluctuate with the current-limiting state and the non-current-limiting state, but the maximum value of the 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 pre-stage circuit operate in the critical current-limiting state, local current limiting can also achieve the effect of dynamic capacitor compensation, but the compensation effect of the critical current-limiting state is the best, and there is no limitation here; in other words, local current limiting greatly reduces the control requirements of the control unit for the pre-stage circuit and can balance between the performance of the control unit and the best compensation effect.

[0033] In summary, if the preset output current value is always too low, it will cause the DC average voltage to continue to decrease, which does not meet the input voltage requirements of the multi-stage inverter. If the preset output current value is always too high, the pre-stage circuit will continuously be in a non-current-limiting state, causing the pre-stage circuit to operate 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 pre-stage circuit, the pre-stage circuit is made to operate between the above two states, critical current limiting or intermittent current limiting, so that the desired fluctuating voltage can appear on the dynamic compensation capacitor. As Figure 7As shown, from top to bottom are the instantaneous waveform diagrams of the output power of the pre-stage circuit in the non-current-limiting state, intermittent current-limiting state, and critical current-limiting state. In the non-current-limiting case, it is equivalent to no additional dynamic compensation. The maximum instantaneous power is 40KW, the minimum is 0KW, and the average power is 20KW. In the intermittent current-limiting state, there is capacitor dynamic compensation. The maximum instantaneous power is 22KW, the minimum is 14KW, and the average power is 20KW. In the critical current-limiting state, there is capacitor dynamic compensation. The maximum instantaneous power is 20.4KW, the minimum 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, while the maximum power of the pre-stage circuit only needs to be 20.4KW and does not need to be set to 40KW. Obviously, this greatly reduces the peak power requirement for the pre-stage circuit, thereby reducing the design cost of the pre-stage circuit and improving the reliability of the overall operation of the pre-stage circuit and the inverter.

[0034] In one embodiment, the minimum value of the capacitance of the dynamic compensation capacitor is: ; wherein, is the maximum average power of the inverter circuit, is a preset proportionality coefficient.

[0035] Specifically, it is known from the foregoing embodiment that when and takes the minimum value, the voltage across the dynamic compensation capacitor at this time is , and this voltage should not be lower than the minimum value of the input voltage of the inverter circuit, and the minimum value of the input voltage of the inverter circuit is where is a pre-configured proportionality coefficient. Considering the actual line voltage drop and inverter modulation ratio, can but is not limited to taking values of 1.05 - 1.1. In the corresponding case, the capacitance of the dynamic compensation capacitor should not be less than ; Further, considering that the output power of the inverter circuit will change with different loads, while the dynamic compensation capacitor in the actual application scenario is selected in advance and will not change due to load changes. Therefore, the dynamic compensation capacitor is preferably selected according to the maximum average power of the inverter circuit, that is, the provided by the above formula is obtained.

[0036] It should be noted that the power regulation system and application scenarios of the multilevel inverter described in the embodiments of the present invention are for more clearly explaining the technical solutions of the embodiments of the present invention, and do not constitute a limitation on the technical solutions provided by the embodiments of the present invention. Those skilled in the art can know that with the evolution of the power regulation system of the multilevel inverter and the emergence of new application scenarios, the technical solutions provided by the embodiments of the present invention are equally applicable to similar technical problems.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A power regulation system for a multilevel inverter, characterized in that The multi-level inverter includes a pre-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, which is connected in parallel between the pre-stage circuit and the inverter circuit, and is used for dynamic charging and discharging to eliminate the power fluctuation of the multi-level inverter, so as to reduce the instantaneous power demand of the pre-stage circuit; A control unit, which is respectively connected to the pre-stage circuit and the inverter circuit, and is used for determining the AC fluctuation voltage output by the pre-stage circuit that matches the dynamic compensation capacitor, and controlling the pre-stage circuit to output the AC fluctuation voltage; Wherein, the frequency of the AC fluctuation voltage is twice the frequency of the output voltage of the inverter circuit, the phase of the AC fluctuation voltage is twice the phase of the output voltage, and the amplitude of the AC fluctuation voltage can be dynamically adjusted.

2. The power regulation system of the multi-level inverter according to claim 1, characterized in that, The control unit specifically determines the AC fluctuation voltage output by the pre-stage circuit that matches the dynamic compensation capacitor in the following manner: Obtain the output voltage waveform of the inverter circuit, and determine the voltage effective value, angular frequency and phase information of the inverter circuit according to the output voltage waveform; Obtain the output current waveform of the inverter circuit, and determine the current effective value of the inverter circuit according to the output current waveform; Obtain the DC average voltage output by the pre-stage circuit and the capacitance of the dynamic compensation capacitor; According to the voltage effective value, the angular frequency, the phase information, the current effective value, the DC average voltage and the capacitance, determine the AC fluctuation voltage output by the pre-stage circuit that matches the dynamic compensation capacitor.

3. The power regulation system of the multi-level inverter according to claim 2, wherein The control unit specifically controls the pre-stage circuit to output the AC fluctuation voltage in the following manner: When the pre-stage circuit adopts an output programmable circuit, an AC fluctuation waveform is injected on the basis of the DC average voltage, wherein 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; Read the output current fluctuation amplitude of the pre-stage circuit, and continuously control the output current fluctuation amplitude until the target current fluctuation condition is met, where the target current fluctuation condition is that the output current fluctuation amplitude is less than or equal to the preset current fluctuation amplitude; Use the output of the AC fluctuation waveform that meets the target current fluctuation condition as the AC fluctuation voltage, and control the pre-stage circuit to output the AC fluctuation voltage on the basis of the DC average voltage.

4. The power regulation system of the multi-level inverter according to claim 2, characterized in that, The control unit specifically controls the pre-stage circuit to output the AC fluctuation voltage in the following manner: When the pre-stage circuit adopts an output voltage closed-loop control circuit and the pre-stage circuit includes a closed-loop control unit, superimpose the instantaneous value of the AC voltage of the pre-stage circuit on the AC fluctuation voltage given by the control unit, so as to control the closed-loop control unit to keep the instantaneous value of the AC voltage consistent with the AC fluctuation voltage based on the PID algorithm; Control the pre-stage circuit to output the AC fluctuation voltage based on the DC average voltage.

5. The power regulation system of the multi-level inverter according to claim 2, characterized in that, The control unit specifically controls the pre-stage circuit to output the AC fluctuation voltage in the following manner: When the pre-stage circuit adopts a constant voltage and current limiting output functional circuit, the control unit obtains the output current of the pre-stage circuit, and when the output current of the pre-stage circuit is greater than the preset output current value, controls the pre-stage circuit to output at the preset output current value, otherwise controls the pre-stage circuit to perform constant voltage output; Read the real-time current limiting state of the pre-stage circuit, and adaptively adjust the preset output current value according to the real-time current limiting state of the pre-stage circuit, so that the pre-stage circuit operates in a critical current limiting state; When the pre-stage circuit operates in a critical current limiting state, control the pre-stage circuit to output the AC fluctuation voltage based on the DC average voltage.

6. The power regulation system of the multi-level inverter according to claim 2, wherein, The control unit calculates the AC fluctuation voltage using the following formula: ； wherein, 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, is the time.

7. The power regulation system of the multi-level inverter according to claim 6, wherein The minimum value of the capacitance is: ； Among them, is the maximum average power of the inverter circuit, is a preset proportionality coefficient.

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

Images