Capacitor voltage balancing control method and device for neutral point clamped boost unit with input inductance, and power electronic converter

Abstract

The application discloses a capacitor voltage equalization control method and device of a neutral point clamped voltage boosting unit with an input inductor and a power electronic converter. The voltage of two series capacitors is collected and a voltage deviation is defined, and the deviation direction is obtained through hysteresis comparison. According to a modulation wave, a current output level interval is determined, and a group of candidate carriers corresponding to the current interval is called from a pre-stored carrier table, the group of carriers containing two carriers with a phase difference of 180 degrees. According to the deviation direction, one of the carriers is selected as a working carrier, and the working carrier is compared with the modulation wave to generate a switch driving signal. When the carrier is switched, only the duration of the redundant switch state is exchanged, and the inductor charge and discharge duty ratio is kept unchanged, so that the capacitor voltage equalization is realized. The device contains a voltage sampling module, a hysteresis comparison processing module and a carrier selection module. The application can be used in other various direct current and alternating current systems, and does not need power calculation and additional voltage equalization circuits, and is simple to control and low in implementation cost.

Description

Technical Field

[0001] This invention relates to power electronic converter control technology, specifically to a capacitor voltage equalization control method, control device, and power electronic converter for a neutral point clamping boost unit with input inductor. Background Technology

[0002] The neutral point clamping unit (NPC) is a mature circuit structure that can improve voltage gain and the number of output levels, and is commonly used in multilevel power converters. A neutral point clamping boost unit with an input inductor typically includes an input inductor, two series capacitors, and multiple power switches. Due to the different charging and discharging times and current paths of the two capacitors, coupled with power device parameter deviations, load variations, and input voltage fluctuations, voltage imbalance between the two capacitors is prone to occur. This capacitor voltage imbalance increases voltage stress on the power devices, affecting output level quality, and in severe cases, may even cause capacitor overvoltage or failure.

[0003] Traditional voltage equalization control methods typically require simultaneous detection of capacitor voltage, inductor current, and output current, and adjust the switching mode using algorithms such as power calculation, closed-loop regulation, or model predictive control. This process is complex and consumes significant controller resources. Some voltage equalization methods also require additional auxiliary switches or voltage equalization circuits, increasing system cost. Summary of the Invention

[0004] This invention proposes a capacitor voltage equalization control method, control device, and power electronic converter for a neutral point clamping boost unit with input inductor, in order to solve the problem of voltage imbalance between the two capacitors in a neutral point clamping boost unit with input inductor.

[0005] The technical solution to achieve the objective of this invention is: a capacitor voltage equalization control method for a neutral point clamping boost unit with an input inductor. The neutral point clamping boost unit includes a DC input power supply, an input inductor, a first capacitor and a second capacitor connected in series, and a switching network. The switching network is used to form different charging and discharging states of the input inductor, as well as the first and second capacitors, including:

[0006] Collect the voltage of the first capacitor and the voltage of the second capacitor;

[0007] The output level range of the current output voltage is determined based on the modulation wave, and a set of candidate carriers corresponding to the output level range is called from the pre-stored carrier table. The set of candidate carriers includes a first carrier and a second carrier. The first carrier and the second carrier have the same amplitude and frequency, and the phase difference between the first carrier and the second carrier is 180°.

[0008] For each output level range, a first redundant switch state combination and a second redundant switch state combination are set. The first redundant switch state combination and the second redundant switch state combination generate the same output level and correspond to the first carrier and the second carrier, respectively. The first redundant switch state combination is used to increase the net charging time of the second capacitor relative to the first capacitor, and the second redundant switch state combination is used to increase the net charging time of the first capacitor relative to the second capacitor.

[0009] Based on the relationship between the voltage of the first capacitor and the voltage of the second capacitor, a working carrier is selected from the first carrier and the second carrier, and the working carrier is compared with the modulated wave to generate the switching drive signal of the switching network.

[0010] The first redundant switch state combination and the second redundant switch state combination have the same total duration of input inductor charging state and the same total duration of input inductor discharging state in each switching cycle, so that carrier switching only changes the charging and discharging time allocation of the first capacitor and the second capacitor, without changing the charging and discharging duty cycle of the input inductor.

[0011] Furthermore, the neutral point clamping boost unit includes an input inductor. First switch Second switch Third switch Fourth switch Fifth Switch First capacitor Second capacitor ;

[0012] The positive terminal of the DC input power supply is connected to the input inductor. Connected to the first node, the negative terminal of the DC input power supply is connected to the common ground;

[0013] The first switch With the second switch The first switch is connected in series between the first node and the common ground. Second switch The connection points form the second node;

[0014] The third switch Connected to the first node and the first capacitor Between the positive terminals, the fifth switch Connected to the common ground and the second capacitor Between the negative electrodes;

[0015] The first capacitor With the second capacitor The first capacitor is connected in series. With the second capacitor The connection point forms the midpoint of the capacitor, and the fourth switch Connect between the second node and the midpoint of the capacitor;

[0016] The first capacitor The positive terminal and the second capacitor The negative terminals respectively constitute the positive and negative output terminals of the neutral point clamping boost unit, and the voltage between the positive and negative output terminals is the output voltage of the neutral point clamping boost unit. .

[0017] Furthermore, the capacitor voltage deviation is defined as:

[0018] ;

[0019] in, The voltage of the first capacitor is... This is the voltage of the second capacitor;

[0020] When the capacitor voltage deviation Greater than the positive hysteresis threshold When this is done, a candidate carrier is selected to increase the net charging time of the first capacitor;

[0021] When the capacitor voltage deviation Less than the negative hysteresis threshold When this is done, a candidate carrier is selected to increase the net charging time of the second capacitor;

[0022] When the capacitor voltage deviation When the current operating carrier is between the negative hysteresis threshold and the positive hysteresis threshold, the current operating carrier remains unchanged.

[0023] Furthermore, a level-shifted sinusoidal pulse width modulation strategy is adopted to compare the sinusoidal modulated wave with multiple triangular carriers shifted along the amplitude direction to generate multi-level output;

[0024] Each output level interval is provided with a triangular carrier and an anti-phase carrier. The triangular carrier and its anti-phase carrier have the same amplitude and frequency, and are 180° out of phase. The triangular carrier or its anti-phase carrier is selected as the current working carrier according to the relationship between the voltage of the first capacitor and the voltage of the second capacitor.

[0025] Furthermore, during the selection of the working carrier and the generation of the switching drive signal, the input inductance is maintained. Charging duty cycle Keep the input inductance unchanged. The volt-second balance is satisfied in each switching cycle, and the charging duty cycle is used to achieve this. Adjust the first capacitor Second capacitor The average voltage;

[0026] Under ideal steady-state conditions, when the voltages of the first and second capacitors reach equilibrium, the following condition is met:

[0027] ;

[0028] in, This refers to the input voltage of the DC input power supply. This is the steady-state average voltage after the first and second capacitors reach equilibrium.

[0029] Furthermore, for achieving voltage equalization control of the first and second capacitors inside the neutral point clamping boost unit, the output level of the neutral point clamping boost unit with input inductor includes at least: ;

[0030] Two sets of candidate carriers are set for the output level interval between adjacent output levels, namely the first carrier pair and the second carrier pair. Each set of candidate carriers includes two carriers with a phase difference of 180°.

[0031] The first carrier pair and interval Correspondingly;

[0032] The second carrier pair and interval Correspondingly.

[0033] A capacitor voltage equalization control device for a neutral point clamping boost unit with an input inductor, wherein the neutral point clamping boost unit includes an input inductor, a first capacitor and a second capacitor connected in series, and a switching network, and the capacitor voltage equalization control device includes:

[0034] A voltage sampling module is connected to the first capacitor and the second capacitor respectively, and is used to collect the voltage of the first capacitor and the voltage of the second capacitor.

[0035] The voltage deviation processing module, connected to the voltage sampling module, is used to obtain the voltage deviation between the first capacitor and the second capacitor, perform hysteresis comparison on the voltage deviation, and output a carrier switching signal.

[0036] The output level range determination module is used to determine the output level range of the current output voltage based on the modulation wave or output voltage.

[0037] The carrier generation module is used to generate a set of candidate carriers for each output level range. Each set of candidate carriers includes a first carrier and a second carrier with the same amplitude and frequency but a phase difference of 180°.

[0038] The carrier selection module is connected to the voltage deviation processing module, the output level range judgment module and the carrier generation module respectively. It is used to receive the carrier switching signal from the voltage deviation processing module and the current output level range information from the output level range judgment module, call a set of candidate carriers corresponding to the current output level range from the carrier generation module, and select the first carrier or the second carrier as the working carrier according to the carrier switching signal.

[0039] The pulse width modulation module, connected to the carrier selection module, is used to compare the working carrier with the modulated wave and generate the switching drive signal for the switching network.

[0040] The first carrier and the second carrier correspond to the first redundant switch state combination and the second redundant switch state combination that generate the same output level, respectively. The first redundant switch state combination and the second redundant switch state combination have the same total duration of input inductor charging state and the same total duration of input inductor discharging state in each switching cycle.

[0041] Furthermore, the voltage sampling module and the voltage deviation processing module include a first isolated sampling operational amplifier. Second isolation sampling operational amplifier Differential operational amplifier Hysteresis comparator First resistor Second resistor Third resistor Fourth resistor Fifth resistor and feedback resistor ;

[0042] First isolation sampling operational amplifier The two input terminals are respectively connected to the first capacitor. The positive and negative terminals are used to collect the voltage of the first capacitor. ;

[0043] Second isolation sampling operational amplifier The two input terminals are respectively connected to the second capacitor. The positive and negative terminals are used to collect the voltage of the second capacitor. ;

[0044] First isolation sampling operational amplifier The output terminal is connected to the first resistor Connected to differential operational amplifier The inverting input terminal of the differential operational amplifier The output terminal is connected to the second resistor Connect to its inverting input;

[0045] Second isolation sampling operational amplifier The output terminal is connected to the third resistor Connected to differential operational amplifier The non-inverting input terminal of the differential operational amplifier The non-inverting input terminal is also connected to a fourth resistor. Connected to reference voltage ;

[0046] The first to fourth resistors satisfy the following:

[0047] ;

[0048] Make the differential operational amplifier The output voltage satisfies:

[0049] ;

[0050] in, The gain coefficient is determined by the sampling ratio of the first isolation sampling operational amplifier and the second isolation sampling operational amplifier, as well as the amplification factor of the differential operational amplifier.

[0051] The differential operational amplifier The output is connected to the hysteresis comparator. The inverting input terminal, reference voltage Through the fifth resistor Connected to hysteresis comparator The non-inverting input terminal of the hysteresis comparator The output terminal is connected to a feedback resistor. Connect it to its non-inverting input to form a positive feedback hysteresis comparator circuit;

[0052] The hysteresis comparator The output terminal is connected to the carrier selection module to output a carrier switching signal to the carrier selection module. .

[0053] A power electronic converter includes a neutral point clamping boost unit with an input inductor, a power conversion unit connected to the output terminal of the neutral point clamping boost unit, and the capacitor equalization control device.

[0054] The power conversion unit is used to convert the output voltage of the neutral point clamp boost unit into the AC or DC output voltage required by the load.

[0055] The power electronic converter is any one of a multilevel inverter, a DC-DC boost converter, or a photovoltaic grid-connected converter;

[0056] The capacitor voltage equalization control device selects candidate carriers with a phase difference of 180°, adjusts the relative charging and discharging time of the first capacitor and the second capacitor in the neutral point clamping boost unit, and achieves voltage equalization of the first capacitor and the second capacitor while keeping the charging and discharging duty cycle of the input inductor constant.

[0057] Furthermore, the power electronic converter is a nine-level common-ground switched capacitor inverter, and the neutral point clamping boost unit constitutes the front-stage boost unit of the nine-level common-ground switched capacitor inverter.

[0058] The output levels of the nine-level common-ground switched capacitor inverter include: The capacitor equalization control device is equipped with four sets of candidate carriers corresponding to four adjacent output level intervals. Each set of candidate carriers includes two carriers with a phase difference of 180°. The first carrier pair corresponds to the interval. and interval Correspondingly; the second carrier pair and interval and interval Correspondingly; the third carrier pair and interval and interval Correspondingly; the fourth carrier pair and interval and interval Correspondingly, a selection is made between two carriers in each group of candidate carriers based on the voltage deviation between the first capacitor and the second capacitor.

[0059] Compared with the prior art, the significant advantages of this invention are: by simply comparing the voltages of the two capacitors and switching carriers with a 180° phase difference, the duration of the corresponding operating mode can be changed, thus achieving voltage balance between the two capacitors; during the voltage equalization process, the input inductor maintains volt-second balance in each switching cycle without changing the duty cycle and voltage gain of the boost unit; this control method does not require complex power calculations or additional power equalization circuits, and has the advantages of simple control and low implementation cost. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the circuit structure of the neutral point clamping boost unit with input inductor of the present invention;

[0061] Figure 2 This is a diagram showing the operating modes of the neutral point clamping boost unit with input inductor of the present invention, wherein (a) is the output +2 level and the inductor is in charging mode; (b) is the output +2 level and the inductor is in discharging mode; (c) is the output +1 level and the inductor is in charging mode; (d) is the output +1 level and the inductor is in discharging mode; (e) is the output 0 level and the inductor is in charging mode; and (f) is the output 0 level and the inductor is in discharging mode.

[0062] Figure 3 This is a schematic diagram of the topology of the present invention applied to a nine-level common-ground switched capacitor inverter;

[0063] Figure 4 This is a schematic diagram of the operating mode duration of the carrier phase shift modulation method of the present invention;

[0064] Figure 5 This is a schematic diagram of the hardware implementation circuit of the voltage equalization control device of the present invention;

[0065] Figure 6 This is a schematic diagram of the simulation results under the condition that the capacitor voltage equalization control method of the present invention is not enabled;

[0066] Figure 7 This is a schematic diagram of the simulation results under the enabled conditions of the capacitor voltage equalization control method of the present invention;

[0067] Figure 8 This is a schematic diagram of the dynamic response of the present invention under the condition of a step change in input voltage. Detailed Implementation

[0068] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0069] This invention proposes a capacitor voltage equalization control method for a neutral point clamping boost unit with an input inductor. The neutral point clamping boost unit includes a DC input power supply and an input inductor. The first capacitor connected in series Second capacitor And a switching network. The switching network is used to form the input inductor charging state, the input inductor discharging state, and the first capacitor. Second capacitor Different charge and discharge states.

[0070] The neutral point clamping boost unit includes a first switch. Second switch Third switch Fourth switch and the fifth switch .

[0071] The positive terminal of the DC input power supply is connected to the input inductor. Connect to the first node; the negative terminal of the DC input power supply is connected to the common ground. First switch. With the second switch The first switch is connected in series between the first node and the common ground. Second switch The connection points form the second node. The third switch... Connected to the first node and the first capacitor Between the positive and negative terminals, the fifth switch Connected to the common ground and the second capacitor Between the negative terminals. First capacitor. With the second capacitor They are connected in series, and the connection point forms the midpoint of the capacitor. Fourth switch. Connected between the second node and the midpoint of the capacitor. First capacitor. The positive terminal and the second capacitor The negative terminals respectively constitute the positive and negative output terminals of the neutral point clamping boost unit, and the voltage between the positive and negative output terminals is the output voltage. .

[0072] The capacitor voltage equalization control method includes the following steps:

[0073] Collect the first capacitor First capacitor voltage Second capacitor Second capacitor voltage ;

[0074] The output level range of the current output voltage is determined based on the modulation wave, and a set of candidate carriers corresponding to the output level range is called from the pre-stored carrier table.

[0075] According to the voltage of the first capacitor Second capacitor voltage Based on the size relationship between them, a candidate carrier is selected from a group of candidate carriers as the working carrier;

[0076] The working carrier wave is compared with the modulated wave to generate the switching drive signal for the switching network.

[0077] The set of candidate carriers includes a first carrier and a second carrier, which have the same amplitude and frequency, and are 180° out of phase.

[0078] For each output level range, a first redundant switch state combination and a second redundant switch state combination are set. The first redundant switch state combination and the second redundant switch state combination produce the same output level and correspond to the first carrier and the second carrier, respectively.

[0079] The first redundant switch state combination is used to increase the second capacitor. Relative to the first capacitor The net charging time, the second redundant switch state combination is used to increase the first capacitor Relative to the second capacitor Net charging time.

[0080] The first redundant switch state combination and the second redundant switch state combination have the same total duration of input inductor charging state and the same total duration of input inductor discharging state in each switching cycle. Therefore, when switching between the first carrier and the second carrier, only the first capacitor is changed. Second capacitor The charging and discharging time allocation is adjusted without changing the input inductance. charge / discharge duty cycle .

[0081] Furthermore, the capacitor voltage deviation is defined. for:

[0082]

[0083] in, The voltage of the first capacitor is... This is the voltage of the second capacitor.

[0084] When the capacitor voltage deviation Greater than the positive hysteresis threshold When, it indicates the voltage of the second capacitor. Higher than the voltage of the first capacitor Selected for adding the first capacitor Candidate carriers for net charging time.

[0085] When the capacitor voltage deviation Less than the negative hysteresis threshold When, it indicates the voltage of the first capacitor. Higher than the voltage of the second capacitor Selected for adding a second capacitor Candidate carriers for net charging time.

[0086] When the capacitor voltage deviation Located at the negative hysteresis threshold With positive hysteresis threshold During this period, the current operating carrier wave is kept constant to avoid the first capacitor voltage. Second capacitor voltage Fluctuations around the equilibrium point cause frequent switching of candidate carriers.

[0087] Furthermore, the capacitor voltage equalization control method employs a level-shifted sinusoidal pulse width modulation strategy, which compares the sinusoidal modulation wave with multiple triangular carrier waves shifted along the amplitude direction to generate multi-level output.

[0088] For each output level interval, a triangular carrier is provided with an anti-phase carrier. The triangular carrier and the anti-phase carrier have the same amplitude and frequency, and their phases differ by 180°. Based on the first capacitor voltage... Second capacitor voltage Based on the size relationship between them, either a triangular carrier or an inverted carrier is selected as the current working carrier.

[0089] In a typical implementation, the output level of the neutral point clamping boost unit with input inductor includes at least: Two sets of candidate carriers are set for the output level interval between adjacent output levels, namely the first carrier pair and the second carrier pair. Each set of candidate carriers includes two carriers with a phase difference of 180°; the first carrier pair and the interval Correspondingly; the second carrier pair and interval Correspondingly.

[0090] During the process of selecting the working carrier and generating the switching drive signal, the switching between the first carrier and the second carrier does not change the input inductance. charge / discharge duty cycle This causes the input inductance to The volt-second balance is satisfied in each switching cycle.

[0091] By input inductance charge / discharge duty cycle Adjust the first capacitor Second capacitor The average voltage. Under ideal steady-state conditions, when the voltage of the first capacitor... With the voltage of the second capacitor When equilibrium is reached, the following conditions must be met:

[0092]

[0093] in, This refers to the input voltage of the DC input power supply. For input inductance The charge / discharge duty cycle, This is the steady-state average voltage after the first and second capacitors reach equilibrium.

[0094] In one specific embodiment, the capacitor voltage equalization control method is used in a nine-level power electronic converter. The output levels of the nine-level power electronic converter include: For the four types of output level intervals between adjacent output levels, a first carrier pair, a second carrier pair, a third carrier pair, and a fourth carrier pair are set. Each group of candidate carriers includes two carriers with a phase difference of 180°.

[0095] The first carrier pair and interval and interval Correspondingly;

[0096] The second carrier pair and interval and interval Correspondingly;

[0097] The third carrier pair and interval and interval Correspondingly;

[0098] The fourth carrier pair and interval and interval Correspondingly.

[0099] This invention also provides a capacitor voltage equalization control device for a neutral point clamping boost unit with an input inductor. The capacitor voltage equalization control device includes a voltage sampling module, a voltage deviation processing module, an output level range judgment module, a carrier generation module, a carrier selection module, and a pulse width modulation module.

[0100] The voltage sampling module is respectively connected to the first capacitor Second capacitor Connection used to acquire the voltage of the first capacitor. Second capacitor voltage .

[0101] The voltage deviation processing module is connected to the voltage sampling module and is used to obtain the voltage of the first capacitor. With the voltage of the second capacitor The difference in capacitor voltage between And for capacitor voltage deviation Perform hysteresis comparison and output carrier switching signal .

[0102] The output level range determination module is used to determine the output level range of the current output voltage based on the modulation wave or output voltage.

[0103] The carrier generation module is used to generate a set of candidate carriers for each output level range. Each set of candidate carriers includes a first carrier and a second carrier with the same amplitude and frequency but a phase difference of 180°.

[0104] The carrier selection module is connected to the voltage deviation processing module, the output level range judgment module, and the carrier generation module, respectively. It is used to retrieve a set of candidate carriers corresponding to the current output level range from the carrier generation module and, based on the carrier switching signal... Choose either the first carrier or the second carrier as the working carrier.

[0105] The pulse width modulation module is connected to the carrier selection module and is used to compare the working carrier with the modulated wave and generate a first switch. Second switch Third switch Fourth switch and the fifth switch The switching drive signal.

[0106] The first carrier and the second carrier correspond to the first redundant switch state combination and the second redundant switch state combination that generate the same output level, respectively. The first redundant switch state combination and the second redundant switch state combination have the same total duration of input inductor charging state and the same total duration of input inductor discharging state in each switching cycle.

[0107] Furthermore, the voltage sampling module and the voltage deviation processing module include a first isolated sampling operational amplifier. Second isolation sampling operational amplifier Differential operational amplifier Hysteresis comparator First resistor Second resistor Third resistor Fourth resistor Fifth resistor and feedback resistor .

[0108] First isolation sampling operational amplifier The two input terminals are respectively connected to the first capacitor. The positive and negative terminals are used to collect the voltage of the first capacitor. .

[0109] Second isolation sampling operational amplifier The two input terminals are respectively connected to the second capacitor. The positive and negative terminals are used to collect the voltage of the second capacitor. .

[0110] First isolation sampling operational amplifier The output terminal is connected to the first resistor Connected to differential operational amplifier The inverting input terminal of the differential operational amplifier The output terminal is connected to the second resistor Connect it to its inverting input.

[0111] Second isolation sampling operational amplifier The output terminal is connected to the third resistor Connected to differential operational amplifier The non-inverting input terminal of the differential operational amplifier The non-inverting input terminal is connected to the fourth resistor. Connected to reference voltage .

[0112] First resistor Second resistor Third resistor and the fourth resistor satisfy:

[0113] Make the differential operational amplifier Output voltage satisfy:

[0114]

[0115] in, For the first isolation sampling operational amplifier Second isolation sampling operational amplifier Sampling ratio and differential operational amplifier The gain coefficient is determined by the amplification factor.

[0116] Differential operational amplifier The output is connected to the hysteresis comparator. The inverting input terminal. Reference voltage. Through the fifth resistor Connected to hysteresis comparator The non-inverting input terminal of the hysteresis comparator The output terminal is connected to a feedback resistor. It is connected to its non-inverting input to form a positive feedback hysteresis comparator circuit.

[0117] Through the fifth resistor Feedback resistor and reference voltage Set capacitor voltage deviation positive hysteresis threshold and negative hysteresis threshold .

[0118] Hysteresis comparator The output terminal is connected to the carrier selection module, and outputs a carrier switching signal to the carrier selection module. .

[0119] The present invention also provides a power electronic converter, including a neutral point clamping boost unit with an input inductor, a power conversion unit connected to the output terminal of the neutral point clamping boost unit, and a capacitor voltage equalization control device.

[0120] The power conversion unit is used to convert the output voltage of the neutral point clamping boost unit into the AC or DC output voltage required by the load. The power electronic converter is any one of a multilevel inverter, a DC-DC boost converter, or a photovoltaic grid-connected converter. The capacitor voltage equalization control device adjusts the first capacitor by selecting a candidate carrier with a 180° phase difference. Second capacitor The relative charge and discharge times, while maintaining the input inductance charge / discharge duty cycle Achieving the first capacitor voltage under unchanged conditions Second capacitor voltage The balance.

[0121] Furthermore, the power electronic converter is a nine-level common-ground switched-capacitor inverter, and the neutral-point clamping boost unit constitutes the front-stage boost unit of the nine-level common-ground switched-capacitor inverter. The capacitor voltage equalization control device is equipped with four sets of candidate carriers corresponding to four adjacent output level ranges, and controls the voltage equalization based on the first capacitor voltage. With the voltage of the second capacitor The difference in capacitor voltage between In each group of candidate carriers, a selection is made between two carriers.

[0122] Example

[0123] To verify the effectiveness of the present invention, the following experimental design was conducted.

[0124] A neutral-point clamping boost unit with an input inductor, such as Figure 1 As shown. Includes DC input power supply. Input inductance First capacitor Second capacitor And switching networks. DC input power supply. via input inductor Connected to the switching network, the first capacitor Second capacitor Series connection. By controlling the on and off states of each power switch in the switching network, the input inductor is kept in a charging or discharging state, and the first and second capacitors are kept in a charging or discharging state, respectively. The operating modes of the unit are as follows: Figure 2 As shown in Table 1.

[0125] Table 1. Operating Status of Neutral Point Clamping Boost Unit

[0126]

[0127] In this context, 1 indicates that the circuit is on, 0 indicates that it is off, and - indicates that the circuit is idle, meaning it is neither charging nor discharging.

[0128] Figure 2 This is a diagram showing the operating modes of the neutral-point clamping boost unit with input inductor of the present invention. In mode (a), the output voltage between the ground wire and terminal A is... In mode (b), the output voltage between the ground wire and terminal A is: In mode (c), the output voltage between the ground wire and terminal A is: In mode (d), the output voltage between the ground wire and terminal A is: In mode (e), the output voltage between the ground wire and terminal B is 0; in mode (f), the output voltage between the ground wire and terminal B is 0. The voltage equalization control device first samples the voltage of the first capacitor. Second capacitor voltage The voltages of the two capacitors are compared. For each output level range, a set of carrier waves with opposite phases is set. and carrier wave and carrier The amplitude and frequency are the same, but the phase difference is 180°. When detected... When the controller selects a carrier wave that can increase the charging time of the second capacitor; when it detects... At that time, the controller selects a carrier wave that can increase the charging time of the first capacitor.

[0129] The aforementioned unit and voltage equalization control method can be used in various DC or AC power supply systems, such as Figure 3 This is a common-ground nine-level topology formed by the aforementioned units. The output voltage is at... and Taking switching between them as an example, the working process is explained as follows: Figure 4 As shown, where It is the output voltage. It is the carrier amplitude. It is the equivalent voltage of the inductor duty cycle. , It is a sinusoidal reference wave. The output level range involves... Figure 2 The modes are (c), (d), (e), and (f). Modes (c) and (f) constitute one set of operating modes, and modes (d) and (e) constitute another set of operating modes. In mode (c), the first capacitor... Continuous discharge, in mode (f), the second capacitor Charging occurs in mode (f). Therefore, increasing the combined duration of modes (c) and (f) can increase the voltage of the second capacitor. Relative to the voltage of the first capacitor Increase. Increasing the duration of modes (d) and (e) can increase the voltage of the first capacitor. Rise. Carrier and carrier The phase difference is 180°. Switching carriers. and carrier The durations of modes (c), (d), (e), and (f) can be interchanged. When the discharge time of the input inductor corresponding to mode (f) is increased, the charging time of the input inductor corresponding to mode (c) is simultaneously increased, keeping the total charging time of the input inductor constant within each switching cycle. Therefore, carrier switching only changes the duration allocation of different operating modes, without changing the charging duty cycle of the input inductor. .

[0130] The hardware circuit of the control method is as follows: Figure 5 As shown, the voltage equalization control device can be implemented using an isolation operational amplifier, a differential amplifier, a hysteresis comparator, and a digital signal processor. First capacitor The voltages of the first and second capacitors are sampled by two isolated operational amplifiers and reduced by a factor of 1 / 20. The reduced voltage signals are then fed into a differential amplifier, which... The corresponding voltage difference signal is amplified 10 times and superimposed with a 2.5V reference voltage. The differential amplifier output signal is fed into a hysteresis comparator, whose reference voltage and hysteresis range are set to 2.5V ± 1.5V. The carrier selection signal output by the comparator is sent to a digital signal processor, which directly selects the carrier corresponding to the current output level range.

[0131] This embodiment was simulated using a nine-level common-ground inverter, and the experimental results are as follows; Figure 6 As shown, the voltage of the first capacitor is [value missing] when voltage equalization control is not used. Second capacitor voltage The deviation between them gradually increases. After adopting the aforementioned pressure equalization control method, as... Figure 7 As shown, the initial voltage deviation between the two capacitors gradually decreases and eventually reaches equilibrium.

[0132] like Figure 8 As shown, when the input voltage When the voltage jumps from 37V to 70V, and then from 70V to 20V, the voltage of the first capacitor... Second capacitor voltage It can still maintain a basic balance, output voltage No significant disturbances were observed, demonstrating the effectiveness and stability of the capacitor voltage equalization control method described in this invention.

[0133] In summary, the voltage equalization control method proposed in this invention is specifically designed for the DC bus capacitor (first capacitor) in a neutral-point clamped multilevel topology. Second capacitor To address the voltage imbalance problem, a simple and low-cost voltage equalization control strategy based on carrier phase shift is proposed. This method compares the DC bus capacitance... and By selecting appropriate carrier signals (0° or 180° phase) in different output level regions and adjusting the duration of complementary state pairs, automatic capacitor voltage balancing can be achieved without changing the inductor volt-second balance and output level. Simulation results show that this method has good dynamic response and steady-state performance, and is suitable for applications such as photovoltaic grid connection with a wide input voltage range.

[0134] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A capacitor voltage equalization control method for a neutral point clamping boost unit with an input inductor, wherein the neutral point clamping boost unit includes a DC input power supply, an input inductor, a first capacitor and a second capacitor connected in series, and a switching network, wherein the switching network is used to form a charging state of the input inductor, a discharging state of the input inductor, and different charging and discharging states of the first capacitor and the second capacitor, characterized in that, include: Collect the voltage of the first capacitor and the voltage of the second capacitor; The output level range of the current output voltage is determined based on the modulation wave, and a set of candidate carriers corresponding to the output level range is called from the pre-stored carrier table. The set of candidate carriers includes a first carrier and a second carrier. The first carrier and the second carrier have the same amplitude and frequency, and the phase difference between the first carrier and the second carrier is 180°. For each output level range, a first redundant switch state combination and a second redundant switch state combination are set. The first redundant switch state combination and the second redundant switch state combination generate the same output level and correspond to the first carrier and the second carrier, respectively. The first redundant switch state combination is used to increase the net charging time of the second capacitor relative to the first capacitor, and the second redundant switch state combination is used to increase the net charging time of the first capacitor relative to the second capacitor. Based on the relationship between the voltage of the first capacitor and the voltage of the second capacitor, a working carrier is selected from the first carrier and the second carrier, and the working carrier is compared with the modulated wave to generate the switching drive signal of the switching network. The first redundant switch state combination and the second redundant switch state combination have the same total duration of input inductor charging state and the same total duration of input inductor discharging state in each switching cycle, so that carrier switching only changes the charging and discharging time allocation of the first capacitor and the second capacitor, without changing the charging and discharging duty cycle of the input inductor.

2. The capacitor voltage equalization control method according to claim 1, characterized in that, The neutral point clamping boost unit includes an input inductor. First switch Second switch Third switch Fourth switch Fifth Switch First capacitor Second capacitor ; The positive terminal of the DC input power supply is connected to the input inductor. Connected to the first node, the negative terminal of the DC input power supply is connected to the common ground; The first switch With the second switch The first switch is connected in series between the first node and the common ground. Second switch The connection points form the second node; The third switch Connected to the first node and the first capacitor Between the positive terminals, the fifth switch Connected to the common ground and the second capacitor Between the negative electrodes; The first capacitor With the second capacitor The first capacitor is connected in series. With the second capacitor The connection point forms the midpoint of the capacitor, and the fourth switch Connect between the second node and the midpoint of the capacitor; The first capacitor The positive terminal and the second capacitor The negative terminals respectively constitute the positive and negative output terminals of the neutral point clamping boost unit, and the voltage between the positive and negative output terminals is the output voltage of the neutral point clamping boost unit. .

3. The capacitor voltage equalization control method according to claim 1, characterized in that, Define the capacitor voltage deviation as: ； in, The voltage of the first capacitor is... This is the voltage of the second capacitor; When the capacitor voltage deviation Greater than the positive hysteresis threshold When this is done, a candidate carrier is selected to increase the net charging time of the first capacitor; When the capacitor voltage deviation Less than the negative hysteresis threshold When this is done, a candidate carrier is selected to increase the net charging time of the second capacitor; When the capacitor voltage deviation When the current operating carrier is between the negative hysteresis threshold and the positive hysteresis threshold, the current operating carrier remains unchanged.

4. The capacitor voltage equalization control method according to claim 1, characterized in that, A level-shifted sinusoidal pulse width modulation strategy is adopted to compare the sinusoidal modulated wave with multiple triangular carriers shifted along the amplitude direction to generate multi-level output; Each output level interval is provided with a triangular carrier and an anti-phase carrier. The triangular carrier and its anti-phase carrier have the same amplitude and frequency, and are 180° out of phase. The triangular carrier or its anti-phase carrier is selected as the current working carrier according to the relationship between the voltage of the first capacitor and the voltage of the second capacitor.

5. The capacitor voltage equalization control method according to claim 1, characterized in that, During the process of selecting the working carrier and generating the switching drive signal, the input inductance is maintained. Charging duty cycle Keep the input inductance unchanged. The volt-second balance is satisfied in each switching cycle, and the charging duty cycle is used to achieve this. Adjust the first capacitor Second capacitor The average voltage; Under ideal steady-state conditions, when the voltages of the first and second capacitors reach equilibrium, the following condition is met: ； in, This refers to the input voltage of the DC input power supply. This is the steady-state average voltage after the first and second capacitors reach equilibrium.

6. The capacitor voltage equalization control method according to claim 1, characterized in that, For achieving voltage equalization control of the first and second capacitors inside the neutral point clamping boost unit, the output level of the neutral point clamping boost unit with input inductor includes at least: ; Two sets of candidate carriers are set for the output level interval between adjacent output levels, namely the first carrier pair and the second carrier pair. Each set of candidate carriers includes two carriers with a phase difference of 180°. The first carrier pair and interval Correspondingly; The second carrier pair and interval Correspondingly.

7. A capacitor equalization control device for a neutral point clamping boost unit with an input inductor, wherein the neutral point clamping boost unit includes an input inductor, a first capacitor and a second capacitor connected in series, and a switching network, characterized in that, The capacitor voltage equalization control device includes: A voltage sampling module is connected to the first capacitor and the second capacitor respectively, and is used to collect the voltage of the first capacitor and the voltage of the second capacitor. The voltage deviation processing module, connected to the voltage sampling module, is used to obtain the voltage deviation between the first capacitor and the second capacitor, perform hysteresis comparison on the voltage deviation, and output a carrier switching signal. The output level range determination module is used to determine the output level range of the current output voltage based on the modulation wave or output voltage. The carrier generation module is used to generate a set of candidate carriers for each output level range. Each set of candidate carriers includes a first carrier and a second carrier with the same amplitude and frequency but a phase difference of 180°. The carrier selection module is connected to the voltage deviation processing module, the output level range judgment module and the carrier generation module respectively. It is used to receive the carrier switching signal from the voltage deviation processing module and the current output level range information from the output level range judgment module, call a set of candidate carriers corresponding to the current output level range from the carrier generation module, and select the first carrier or the second carrier as the working carrier according to the carrier switching signal. The pulse width modulation module, connected to the carrier selection module, is used to compare the working carrier with the modulated wave and generate the switching drive signal for the switching network. The first carrier and the second carrier correspond to the first redundant switch state combination and the second redundant switch state combination that generate the same output level, respectively. The first redundant switch state combination and the second redundant switch state combination have the same total duration of input inductor charging state and the same total duration of input inductor discharging state in each switching cycle.

8. The capacitor voltage equalization control device according to claim 7, characterized in that, The voltage sampling module and voltage deviation processing module include a first isolation sampling operational amplifier. Second isolation sampling operational amplifier Differential operational amplifier Hysteresis comparator First resistor Second resistor Third resistor Fourth resistor Fifth resistor and feedback resistor ; First isolation sampling operational amplifier The two input terminals are respectively connected to the first capacitor. The positive and negative terminals are used to collect the voltage of the first capacitor. ; Second isolation sampling operational amplifier The two input terminals are respectively connected to the second capacitor. The positive and negative terminals are used to collect the voltage of the second capacitor. ; First isolation sampling operational amplifier The output terminal is connected to the first resistor Connected to differential operational amplifier The inverting input terminal of the differential operational amplifier The output terminal is connected to the second resistor Connect to its inverting input; Second isolation sampling operational amplifier The output terminal is connected to the third resistor Connected to differential operational amplifier The non-inverting input terminal of the differential operational amplifier The non-inverting input terminal is also connected to a fourth resistor. Connected to reference voltage ; The first to fourth resistors satisfy the following: ； Make the differential operational amplifier The output voltage satisfies: ； in, The gain coefficient is determined by the sampling ratio of the first isolation sampling operational amplifier and the second isolation sampling operational amplifier, as well as the amplification factor of the differential operational amplifier. The differential operational amplifier The output is connected to the hysteresis comparator. The inverting input terminal, reference voltage Through the fifth resistor Connected to hysteresis comparator The non-inverting input terminal of the hysteresis comparator The output terminal is connected to a feedback resistor. Connect it to its non-inverting input to form a positive feedback hysteresis comparator circuit; The hysteresis comparator The output terminal is connected to the carrier selection module to output a carrier switching signal to the carrier selection module. .

9. A power electronic converter, characterized in that, It includes a neutral point clamping boost unit with an input inductor, a power conversion unit connected to the output terminal of the neutral point clamping boost unit, and the capacitor voltage equalization control device as described in claim 7 or 8. The power conversion unit is used to convert the output voltage of the neutral point clamp boost unit into the AC or DC output voltage required by the load. The power electronic converter is any one of a multilevel inverter, a DC-DC boost converter, or a photovoltaic grid-connected converter; The capacitor voltage equalization control device selects candidate carriers with a phase difference of 180°, adjusts the relative charging and discharging time of the first capacitor and the second capacitor in the neutral point clamping boost unit, and achieves voltage equalization of the first capacitor and the second capacitor while keeping the charging and discharging duty cycle of the input inductor constant.

10. The power electronic converter according to claim 9, characterized in that, The power electronic converter is a nine-level common-ground switched capacitor inverter, and the neutral point clamping boost unit constitutes the front-stage boost unit of the nine-level common-ground switched capacitor inverter. The output levels of the nine-level common-ground switched capacitor inverter include: The capacitor equalization control device is equipped with four sets of candidate carriers corresponding to four adjacent output level intervals. Each set of candidate carriers includes two carriers with a phase difference of 180°. The first carrier pair corresponds to the interval. and interval Correspondingly; the second carrier pair and interval and interval Correspondingly; the third carrier pair and interval and interval Correspondingly; the fourth carrier pair and interval and interval Correspondingly, a selection is made between two carriers in each group of candidate carriers based on the voltage deviation between the first capacitor and the second capacitor.

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