An inverter modulation method

Abstract

The application discloses an inverter modulation method, comprising the following steps: obtaining the electric quantity parameter and the environmental parameter of the inverter; selecting the modulation mode of the inverter according to the comparison result of the electric quantity parameter and the environmental parameter with the set threshold; the modulation mode comprises a first modulation mode and a second modulation mode, the first modulation mode is adjusting the driving signal of the corresponding switch bridge arm of the inverter, and the second modulation mode is setting the dead-time compensation time of the switch bridge arm. In the case of not increasing additional hardware devices, two kinds of modulation modes are set, and according to the change of the two parameters, the modulation mode can be flexibly selected to ensure that the inverter can maintain high efficiency and stability under various environmental conditions. The dead-time compensation and narrow pulse suppression are combined, the situation that only adjusting one problem leads to another problem aggravation is avoided, the performance of the inverter under different working conditions is increased, and the problems caused by the narrow pulse and the dead-time effect are solved.

Description

Technical Field

[0001] This application relates to the technical field of power electronics technology, and more specifically, to a modulation method for inverter dead zone and narrow pulse suppression. Background Technology

[0002] Currently, in the inverter technology field, dead time is mainly set to prevent the upper and lower bridge arms from conducting simultaneously. Simultaneous conduction of the upper and lower bridge arms would lead to a short circuit. However, excessively long dead time can cause inverter output waveform distortion, thus affecting the quality of the output waveform. Dead time compensation can help reduce waveform distortion caused by dead time. In PWM modulation, narrow pulses typically refer to pulses that switch frequently within a short period. This increases switching losses and may lead to electromagnetic interference problems. The goal of narrow pulse suppression is to avoid excessive narrow pulses through proper modulation, thereby reducing losses and improving system efficiency.

[0003] In existing technologies, adaptive algorithms are used to balance dead zone compensation and narrow pulse suppression. Adaptive algorithms achieve flexible compensation and suppression under different conditions by dynamically adjusting the parameters of signal processing.

[0004] However, existing technologies have the following drawbacks: dead-time compensation and narrow-pulse suppression both affect the inverter's switching frequency and efficiency. While a higher switching frequency can improve waveform quality, it also increases switching losses, leading to more heat generation. Furthermore, both dead-time compensation and narrow-pulse suppression involve rapid changes in current and voltage, which can affect the stability of the bus voltage. Fluctuations in the inverter's bus voltage can cause system instability and affect load operation. Therefore, it is essential to provide a modulation method that performs dead-time compensation and narrow-pulse suppression based on bus voltage, modulation ratio, system temperature, and duty cycle. Summary of the Invention

[0005] One objective of this application is to provide an inverter modulation method that selects the optimal modulation mode based on the actual situation of the inverter in order to reduce the impact of dead zone compensation and narrow pulse suppression.

[0006] To achieve the above objectives, the technical solution adopted in this application is as follows: an inverter modulation method, comprising the following steps: acquiring the inverter's power parameters and environmental parameters; selecting the inverter's modulation mode based on the comparison results of the power parameters and environmental parameters with set thresholds; the modulation mode includes a first modulation mode and a second modulation mode, wherein the first modulation mode is: adjusting the drive signal of the corresponding switch arm of the inverter, and the second modulation mode is: setting the dead time compensation time of the switch arm.

[0007] As a preferred option, the modulation mode selection for the inverter includes the following process: calculating the modulation ratio using the power parameters and comparing the obtained modulation ratio with a set modulation ratio threshold; if the modulation ratio is lower than the set modulation ratio threshold, the inverter will select the first modulation mode for modulation; otherwise, the modulation selection of the inverter will be further judged in conjunction with environmental parameters.

[0008] As another preferred option, the power parameters include the peak grid voltage U on the AC side of the inverter. ac_max and the DC side bus voltage U dc The modulation ratio m is calculated as follows: .

[0009] Further optimization involves using the inverter's system temperature as the environmental parameter. The process of determining the inverter's modulation selection based on the system temperature includes the following steps: comparing the system temperature with a set temperature threshold; if the system temperature is lower than the set temperature threshold, the inverter will select the first modulation mode; otherwise, the modulation selection will be determined by combining the inverter's duty cycle.

[0010] Further optimization involves raising the DC bus voltage of the inverter before the system temperature is lowered below a set temperature threshold to control the inverter to use the first modulation mode.

[0011] Further optimization involves determining the inverter's modulation selection based on the duty cycle, including the following process: calculating the inverter's duty cycle in real time based on the power parameters and comparing it with a set duty cycle threshold; if the inverter's duty cycle is greater than the duty cycle threshold, the inverter will select the first modulation mode for modulation, otherwise it will select the second modulation mode for modulation.

[0012] Further optimization yields a duty cycle threshold of 0.2.

[0013] Further optimization involves using a given duty cycle threshold D and grid voltage U. ac Calculate the first voltage value U of the DC side bus voltage. dc0 First voltage value U dc0 The calculation method is as follows: U dc0 =U ac / D; The first voltage value U obtained dc0 Substitute the values ​​into the formula for calculating the modulation ratio m, and denote the obtained modulation ratio m as the modulation ratio threshold M.

[0014] Further preferred, the inverter is connected to the grid, and the switching bridge arm includes a first power switch and a second power switch connected in series. The first power switch is connected to the positive terminal of the bus, and the second power switch is connected to the negative terminal of the bus. The first power switch includes a first transistor Q1 and a first diode D1, and the second power switch includes a second transistor Q2 and a second diode D2. Controlling the inverter to execute a first modulation mode specifically includes the following steps: when the grid is in the positive half-cycle, cancel the drive signal of the second diode D2; when the grid is in the negative half-cycle, cancel the drive signal of the first diode D1.

[0015] Further optimization involves optimizing the electrical parameters, including the dead time, turn-on delay, and turn-off delay of each switching device in the switching bridge arm. When controlling the inverter to execute the second modulation mode, the dead-time compensation time is calculated based on the dead time, turn-on delay, and turn-off delay. The dead-time compensation time is used to compensate the modulation waveform, thereby suppressing the voltage error caused by the dead time and device operation delay. The dead-time compensation time t... com The specific calculation formula is as follows: When the current flowing through the switch bridge arm is greater than 0, the dead time compensation time is calculated as follows: t com =t d +t on- t off When the current flowing through the switch bridge arm is less than 0, the dead time compensation time is calculated as follows: t com =t off -t d -t on ; where t on For conduction delay, t d For dead time, t off For disconnection delay.

[0016] Compared with the prior art, the beneficial effects of this application are as follows:

[0017] Without adding extra hardware, two modulation modes are set up, and the modulation mode can be flexibly selected according to the changes in power parameters and environmental parameters. This ensures that the inverter can maintain high efficiency and stability under various environmental conditions. By combining dead-zone compensation and narrow-pulse suppression, the situation of exacerbating the other problem by adjusting only one problem is avoided. This improves the inverter's performance under different operating conditions and solves the problems caused by narrow pulse and dead-zone effects. Attached Figure Description

[0018] Figure 1 This is a flowchart of the inverter modulation method.

[0019] Figure 2 This is a circuit diagram of an inverter system.

[0020] Figure 3 This is a schematic diagram of the waveforms of the drive signal under different modulation ratios.

[0021] Figure 4 This is a waveform diagram of the drive signal with dead time.

[0022] Figure 5 This is a waveform diagram of a drive signal without dead time.

[0023] Figure 6 A schematic diagram of the waveform of the drive signal for dead-time compensation.

[0024] In the diagram: 110, first power switch; 120, second power switch. Detailed Implementation

[0025] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0026] In the description of this application, it should be noted that the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., which indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of this application.

[0027] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0028] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0029] To facilitate understanding of the technical solution of this application, the dead-time effect and narrow-pulse phenomenon of inverters are explained below. First, the dead-time effect of inverters is due to the time delay between the switching of the power switches during the switching process. This causes the output voltage to fail to accurately follow the input voltage change at certain moments, resulting in waveform distortion. At the same time, to avoid short-circuit current between the switching elements, a dead time is introduced between the two switches to ensure that the next switch is allowed to turn on only after the previous switch has been completely turned off. Second, the narrow-pulse phenomenon refers to the brief and sharp current or voltage fluctuations that appear in the inverter output waveform. These fluctuations affect the output quality of the inverter and cause high-frequency harmonic components in the spectrum.

[0030] Therefore, based on the above problems, this application proposes an inverter modulation method that sets two modulation modes without adding extra hardware, and selects between the two modulation modes according to the actual situation of the inverter, combining dead-time compensation and narrow-pulse suppression. This avoids the situation where adjusting only one problem will aggravate the other problem, thereby increasing the performance of the inverter under different operating conditions and solving the problems caused by narrow-pulse and dead-time effects.

[0031] The principle of the inverter modulation method provided in this application includes the following steps: Figure 1 As shown, the inverter's power parameters and environmental parameters are obtained; based on the comparison results of the power parameters and environmental parameters with set thresholds, the modulation mode of the inverter is selected. The modulation mode selection includes a first modulation mode and a second modulation mode. The first modulation mode involves adjusting the drive signal of the corresponding switching arm of the inverter, and the second modulation mode involves setting the dead-time compensation time of the switching arm.

[0032] As can be seen from the principle of the present application, during the modulation process of the inverter, the electrical parameters and environmental parameters are important factors in determining the modulation mode selection. Based on the changes in these parameters, the modulation mode can be flexibly selected to ensure that the inverter can maintain high efficiency and stability under various environmental conditions.

[0033] The modulation method will be explained in detail below. Assuming that the inverter is connected to the power grid and is in operation, the inverter obtains power parameters and environmental parameters in real time through current sensors, voltage sensors and temperature sensors. The current sensors, voltage sensors and temperature sensors are all common models that meet the usage conditions, and will not be elaborated on here.

[0034] In this embodiment, the inverter obtains the peak voltage U of the AC grid through a voltage sensor. ac_max and DC side bus voltage U dc Peak grid voltage Uac_max The bus voltage U is acquired in real time by a voltage sensor. dc It is monitored in real time by a DC voltage sensor.

[0035] The electrical parameters include the peak grid voltage U on the AC side of the inverter. ac_max and DC side bus voltage U dc The modulation ratio m is calculated as follows: .

[0036] It is understandable that after obtaining the modulation ratio m through the above calculation formula, the modulation ratio m is compared with the modulation ratio threshold M. When the modulation ratio m is less than the modulation ratio threshold M, the first modulation mode is used for modulation. According to the calculation formula of the modulation ratio m, the DC side bus voltage U dc The larger the value, the smaller the modulation ratio m.

[0037] In this embodiment, as Figure 3 As shown, the grid voltage U ac The lower the voltage, the lower the DC bus voltage U. dc The higher the modulation ratio (m), the lower the modulation ratio (m). When the modulation ratio (m) is low, the inverter will not generate narrow pulses because, during frequency modulation, a low modulation ratio usually means a smaller frequency offset and less frequency change in the carrier. In other words, a low modulation ratio results in a relatively small range of frequency offset, with less high-frequency components in the generated frequency spectrum, and the spectrum mainly concentrated in the lower frequency range. When the modulation ratio is low, the waveform of the frequency-modulated signal changes slowly in the time domain, and the pulse duration is longer, resulting in wide pulses. Therefore, when the modulation ratio (m) is less than the modulation ratio threshold (M), only the drive signal of the corresponding bridge arm switch of the inverter needs to be adjusted.

[0038] Specifically, such as Figure 2 As shown, the inverter includes three sets of switch arms, each corresponding to one of the three phases of the power grid. Each switch arm includes a first power switch 110 and a second power switch 120 connected in series. The first power switch 110 is connected to the positive terminal of the bus, and the second power switch 120 is connected to the negative terminal of the bus. The first power switch 110 includes a first transistor Q1 and a first diode D1, and the second power switch 120 includes a second transistor Q2 and a second diode D2. Under normal inverter operation, the positive half-cycle of the power grid requires the output of positive current from the first transistor Q1 and the second diode D2; the negative half-cycle requires the output of the first diode D1 and the second transistor Q2.

[0039] It is understandable that when the inverter does not use the first modulation mode, the inverter waveform is as follows: Figure 4The figure shows the output voltage of phase A of the power grid and the error voltage waveform due to the dead time effect. GaH* and GaL* are the ideal driving waveforms of the first power switch 110 and the second power switch 120, respectively, and GaH1 and GaL1 are the waveforms considering the dead time t. d Device turn-on delay t on and shutdown delay t off The driving waveform; V a * and V a V represents the ideal voltage and actual voltage of phase A; err For voltage error; T s For one carrier cycle; ideally, the first power switch 110 should be turned on while the second power switch 120 is turned off, thus obtaining the waveforms shown in GaH* and GaL*. However, during the switching process, the first power switch 110 and the second power switch 120 experience a certain delay, resulting in the waveforms shown in GaH1 and GaL1. Therefore, V a * and V a A voltage drop V was generated between them. err .

[0040] When the inverter adopts the first modulation mode, the drive signal of the second transistor Q2 is canceled when the grid is in the positive half-cycle; the drive signal of the first transistor Q1 is canceled when the grid is in the negative half-cycle. Based on the above operations, the following can be obtained: Figure 5 The waveform shown, taking only the first power switch 110 as an example, V a * and V a There is no voltage drop between them, V err The fact that the voltage is 0 indicates that the first modulation mode provided in this application can effectively eliminate voltage loss.

[0041] However, when the modulation ratio m is greater than the modulation ratio threshold M, multiple factors need to be considered. If the DC bus voltage increases, the inverter's DC duty cycle will be higher, the switching transistor's conduction loss will be greater, and the system will generate more heat, causing the inverter's system temperature to rise. In other words, the temperature change can reflect the specific situation of the DC bus voltage. Therefore, it is very necessary to analyze the changes in the DC bus voltage from the perspective of the inverter's system temperature.

[0042] In this embodiment, a temperature sensor is installed on the inverter to obtain the inverter's system temperature t, such as the temperature of the inverter's heat sink or the ambient temperature. The system temperature t mainly reflects the operating temperature of the electronic components inside the inverter, and changes in temperature will affect the inverter's switching performance and modulation accuracy.

[0043] The system temperature t is compared with the temperature threshold T to further determine the inverter's operating state, and the maximum system temperature T of the inverter is set as the threshold. max The derating is 80% as the temperature threshold T, and the maximum system temperature T is... max The recommended values ​​can be obtained by consulting the inverter's technical specifications. These values ​​are based on factors such as the inverter's internal components, heat dissipation capacity, and environmental adaptability, and will not be elaborated upon here. When the system temperature t is less than the temperature threshold T, the DC bus voltage of the inverter is increased to suppress the generation of narrow pulses. When the system temperature t is greater than the temperature threshold T, it indicates that the switching frequency of the inverter's power switch is higher, generating more heat. The switching frequency of the power switch is closely related to the duty cycle; therefore, it is essential to combine this with the inverter's duty cycle d for modulation selection and judgment.

[0044] It's understandable that the duty cycle d is the ratio of the on-time of the switching element to the total time of the entire cycle. When the duty cycle d is greater than the duty cycle threshold D, the larger the duty cycle d, the longer the high-level duration of the signal, resulting in a longer pulse. Therefore, the signal remains high for a longer period within a cycle, producing a wide pulse instead of a narrow pulse. Thus, when the duty cycle d is greater than the duty cycle threshold D, selecting the first modulation mode only requires adjusting the drive signal of the corresponding switching arm of the inverter.

[0045] When the duty cycle d is less than the duty cycle threshold D, the smaller the duty cycle d, the shorter the duration of the high level of the signal, resulting in a shorter pulse and thus a narrow pulse. Therefore, it is necessary to select the second modulation mode for modulation.

[0046] It should be understood that the specific value of the duty cycle threshold D can be selected according to the actual needs of those skilled in the art. For example, in this embodiment, the preferred value of the duty cycle threshold D is 0.2. That is to say, the conduction time of the switching device accounts for 20% of one cycle. By setting the duty cycle d to a smaller value, the conduction time of the switching element can be effectively reduced, thereby reducing the losses during switching operation. At the same time, the switching device will experience greater thermal stress during a longer conduction time. A shorter conduction time can help reduce the heat accumulation of the switching device, reduce the risk of overheating, and thus extend the service life of the equipment.

[0047] In this embodiment, the modulation ratio threshold M specifically includes the following process: The first voltage value U of the DC-side bus voltage is calculated using a given duty cycle threshold D and switching period T. dc0 The first voltage value U obtained dc0 Substitute the values ​​into the formula for calculating the modulation ratio m, and denote the resulting modulation ratio m as the modulation ratio threshold M. First voltage value U dc0 The calculation method is as follows: U dc0 =Uac *T / T on The modulation ratio threshold M is calculated as follows: .

[0048] Among them, T on The duration of the positive half-cycle drive signal is represented by T, which represents the switching period; when calculating the modulation ratio threshold M, T... on / T=D.

[0049] In this embodiment, as Figure 6 As shown, when the current i flowing through the switch bridge arm a When the voltage is greater than 0, ignoring the effect of the voltage drop of the device itself, and assuming the control signal is an ideal drive signal, at time t0, the first power switch 110 is turned on, the second power switch 120 is turned off, and the voltage of phase A rises to V. dc However, due to the existence of dead time t d The second power switch 120 is turned on with a delay of t. on The second power switch 120 turns on at time t2. During the time interval from t1 to t2, current flows through other paths in the circuit or reverses, resulting in current loss. Ideally, at time t3, the first power switch 110 turns off and the second power switch 120 turns on, and the voltage of phase A begins to drop. However, due to the turn-off delay t of the first power switch 110... off This causes the first power switch 110 to turn off only at time t4, resulting in an increase in voltage, according to V a * and V a The waveform diagram shows that a voltage drop occurred.

[0050] From the above analysis, we can see that the voltage error caused by dead time and power switching delay can be calculated using the following formula: when i a When V > 0, err =(t off -t d -t on V dc / T s ; when i a When <0, V err =(t off -t d -t on V dc / T s .

[0051] Therefore, when using the second modulation mode, the dead time t is taken into account. d Conduction delay t on and disconnection delay t off The dead zone compensation time t that needs to be compensatedcom The value is obtained through the following formula: when i a When t > 0, com =t d +t on- t off ; when i a When <0, t com =t off -t d -t on This eliminates voltage loss.

[0052] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. An inverter modulation method, characterized in that, Includes the following steps: The inverter's power parameters are obtained, and the modulation ratio is calculated using the power parameters. The obtained modulation ratio is then compared with a set modulation ratio threshold. If the modulation ratio is lower than the modulation ratio threshold, the inverter will select the first modulation mode for modulation. Otherwise, the system temperature will be considered when determining the inverter's modulation selection. The system temperature is compared with a set temperature threshold. The duty cycle of the inverter is calculated in real time based on the power parameters and compared with a set duty cycle threshold. Based on the comparison result, the modulation mode of the inverter is selected. The modulation mode includes a first modulation mode and a second modulation mode. The first modulation mode is to adjust the drive signal of the corresponding switch arm of the inverter. The second modulation mode is to set the dead time compensation time of the switch arm. If the system temperature is higher than the temperature threshold and the duty cycle is lower than the duty cycle threshold, the second modulation mode is selected; otherwise, the first modulation mode is selected.

2. The inverter modulation method as described in claim 1, characterized in that, The electrical parameters include the peak grid voltage U on the AC side of the inverter. ac_max and the DC side bus voltage U dc The modulation ratio m is calculated as follows: .

3. The inverter modulation method as described in claim 1, characterized in that, Before the system temperature is lower than the temperature threshold to control the inverter to use the first modulation mode for modulation, the DC bus voltage of the inverter is first increased.

4. The inverter modulation method as described in claim 1, characterized in that, The duty cycle threshold is 0.

2.

5. The inverter modulation method as described in claim 2, characterized in that, The calculation process for the modulation ratio threshold M is as follows: Based on the given duty cycle threshold D and the grid voltage U... ac The first voltage value U of the DC-side bus voltage is calculated. dc0 ; First voltage value U dc0 The calculation formula is as follows: U dc0 =U ac / D; The obtained first voltage value U dc0 The bus voltage U on the DC side dc Substitute the values ​​into the formula for calculating the modulation ratio m, and record the obtained modulation ratio m as the modulation ratio threshold M.

6. The inverter modulation method according to any one of claims 1-5, characterized in that, The inverter is connected to the power grid. The switching bridge arm includes a first power switch and a second power switch connected in series. The first power switch is connected to the positive terminal of the bus, and the second power switch is connected to the negative terminal of the bus. The first power switch includes a first transistor Q1 and a first diode D1, and the second power switch includes a second transistor Q2 and a second diode D2. Controlling the inverter to execute the first modulation mode specifically includes the following steps: When the power grid is in the positive half-cycle, the drive signal of the second transistor Q2 is canceled; When the power grid is in the negative half-cycle, the drive signal of the first transistor Q1 is canceled.

7. The inverter modulation method according to any one of claims 1-5, characterized in that, The electrical parameters include the dead time, turn-on delay, and turn-off delay of each switching device in the switching bridge arm; when controlling the inverter to execute the second modulation mode, the dead time compensation time is calculated based on the dead time, the turn-on delay, and the turn-off delay; the modulation waveform is compensated by the dead time compensation time, thereby suppressing the voltage error caused by the dead time and device operation delay; The dead zone compensation time t com The specific calculation formula is as follows: When the current flowing through the switch bridge arm is greater than 0, the dead time compensation time is calculated as follows: t com =t d +t on- t off ; When the current flowing through the switch bridge arm is less than 0, the dead time compensation time is calculated as follows: t com =t off -t d -t on ; Among them, t on For the conduction delay, t d Let t be the dead time. off The disconnection delay is specified.

Images