Inverter modulation method

Abstract

The invention discloses an inverter modulation method. The method comprises the following steps: obtaining an electric quantity parameter and an environment parameter of an inverter; selecting a modulation mode of the inverter according to comparison results of the electric quantity parameter and the environment parameter with a set threshold value; the modulation mode comprises a first modulation mode and a second modulation mode, the first modulation mode is to adjust a driving signal of a switch bridge arm corresponding to the inverter, and the second modulation mode is to set dead zone compensation time of the switch bridge arm. Two modulation modes are set under the condition that no extra hardware device is added, the modulation modes can be flexibly selected according to the change condition of two parameters so as to ensure that the inverter can keep high efficiency and stability under various environmental conditions, dead-zone compensation and narrow pulse suppression are combined, the problem that only one of the dead-zone compensation and the narrow pulse suppression is adjusted is avoided, and the control efficiency of the inverter is improved. Therefore, the performance of the inverter under different working conditions can be improved, and the problems caused by narrow pulse and dead zone effect can be solved.

Description

Technical Field

[0001] The present application relates to the technical field of power electronics technology, and in particular to a modulation method for inverter dead zone and narrow pulse suppression. Background Art

[0002] At present, in the field of inverter technology, the dead time is mainly set to prevent the upper and lower bridge arms from being turned on at the same time. If the upper and lower bridge arms are turned on at the same time, a short circuit will occur. However, if the dead time is too long, the inverter output waveform will be distorted, thereby affecting the quality of the output waveform. Dead time compensation can help reduce the waveform distortion caused by the dead time. In PWM modulation, narrow pulses usually refer to pulses that are frequently switched in a short period of time, which will increase switching losses and may cause electromagnetic interference problems. The goal of narrow pulse suppression is to avoid excessive narrow pulses through reasonable modulation, thereby reducing losses and improving system efficiency.

[0003] In the prior art, an adaptive algorithm is used to balance dead zone compensation and narrow pulse suppression. The adaptive algorithm dynamically adjusts signal processing parameters to achieve flexible compensation and suppression under different conditions.

[0004] However, the existing technical means have the following defects: dead zone compensation and narrow pulse suppression will affect the switching frequency and efficiency of the inverter. Although a higher switching frequency can improve the waveform quality, it will increase switching losses, thereby causing more heat generation. At the same time, dead zone compensation and narrow pulse suppression both involve rapid changes in current and voltage, which will have a certain impact on the stability of the bus voltage. The bus voltage fluctuation of the inverter may cause system instability and affect the operation of the load. Therefore, it is very necessary to provide a modulation method for performing dead zone compensation and narrow pulse suppression on the system according to the bus voltage, modulation ratio, system temperature, and duty cycle. Summary of the invention

[0005] One object of the present application is to provide an inverter modulation method, which selects the best modulation mode according to the actual situation of the inverter to reduce the influence of dead zone compensation and narrow pulse suppression.

[0006] To achieve the above objectives, the technical solution adopted in the present application is: an inverter modulation method, comprising the following steps: obtaining the power parameters and environmental parameters of the inverter; selecting the modulation mode of the inverter according to the comparison results of the power parameters and environmental parameters with the set thresholds respectively; the modulation mode includes a first modulation mode and a second modulation mode, the first modulation mode is: adjusting the drive signal of the corresponding switch bridge arm of the inverter, and the second modulation mode is: setting the dead zone compensation time of the switch bridge arm.

[0007] As a preferred embodiment, the modulation mode selection for the inverter includes the following process: calculating the modulation ratio through the power parameters, and comparing the obtained modulation ratio with the 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 continue to be judged in combination with the environmental parameters.

[0008] As another preferred embodiment, the power parameter includes the peak value of the grid voltage U on the AC side of the inverter. ac_max And the DC bus voltage U dc ; The modulation ratio m is calculated as:

[0009] Further preferably, the environmental parameter is the system temperature of the inverter; judging the modulation selection of the inverter based on the system temperature includes the following process: 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 for modulation; otherwise, the modulation selection will be judged in combination with the duty cycle of the inverter.

[0010] Further preferably, before the system temperature is lower than a set temperature threshold to control the inverter to adopt the first modulation mode for modulation, the DC side bus voltage of the inverter is first increased.

[0011] Further preferably, judging the modulation selection of the inverter based on the duty cycle includes the following process: calculating the duty cycle of the inverter in real time according to the power parameters and comparing it with the set duty cycle threshold; if the duty cycle of the inverter is greater than the duty cycle threshold, the inverter will select the first modulation mode for modulation, otherwise select the second modulation mode for modulation.

[0012] More preferably, the duty cycle threshold is 0.2.

[0013] Further preferably, by given duty cycle threshold D and grid voltage U ac , calculate the first voltage value U of the DC bus voltage dc0 ; The first voltage value U dc0 The calculation method is: U dc0 =U ac *D; the first voltage value U dc0 Substitute the modulation ratio m into the calculation formula for calculation, and record the obtained modulation ratio m as the modulation ratio threshold M.

[0014] Further preferably, the inverter is connected to the power grid, the switch bridge arm includes a first power switch and a second power switch connected in series, the first power switch is connected to the positive end of the bus, the second power switch is connected to the negative end 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 a positive half cycle, canceling the drive signal of the second diode D2; when the power grid is in a negative half cycle, canceling the drive signal of the first diode D1.

[0015] Further preferably, the electrical quantity parameters include the dead time, on-delay and off-delay of each switch device in the switch bridge arm; when controlling the inverter to execute the second modulation mode, the dead time compensation time is calculated according to the dead time, on-delay and off-delay; the modulation waveform is compensated by the dead time compensation time, thereby suppressing the voltage error caused by the dead time and the device action 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 zone compensation time is calculated as: t com =t d +t on- t off ; When the current flowing through the switch bridge arm is less than 0, the dead zone compensation time is calculated as: t com =t off -t d -t on ; where t on is the turn-on delay, t d is the dead time, t off Delay for disconnection.

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

[0017] Without adding additional hardware devices, two modulation modes are set. According to the changes in power parameters and environmental 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 zone compensation and narrow pulse suppression are combined to avoid the situation where only one of the problems is adjusted, which will lead to the aggravation of the other problem. The performance of the inverter under different working conditions is increased, and the problems caused by narrow pulse and dead zone effects are solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flow chart of an inverter modulation method;

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

[0020] Figure 3 Schematic diagram of the waveform of the driving signal under different modulation ratios;

[0021] Figure 4 Schematic diagram of the waveform of a driving signal with a dead zone;

[0022] Figure 5 Schematic diagram of the waveform of the driving signal without dead zone;

[0023] Figure 6 Schematic diagram of the waveform of the driving signal for dead zone compensation.

[0024] In the figure: 110, a first power switch; 120, a second power switch. DETAILED DESCRIPTION

[0025] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0026] In the description of the present application, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the accompanying drawings, which are only for the convenience of narrating the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and cannot be understood as limiting the specific scope of protection of the present application.

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

[0028] The terms "including" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0029] In order to facilitate the understanding of the technical solution of the present application, the dead zone effect and narrow pulse phenomenon of the inverter are explained below. First, the dead zone effect of the inverter is caused by a certain time delay in the conduction and shutdown of the power switch of the inverter during the switching process, resulting in the voltage at the output end being unable to accurately follow the voltage change at the input end at certain moments, thereby causing waveform distortion. At the same time, in order to avoid short-circuit current between the conduction and shutdown of the switching element, a dead zone time is introduced between the two switches to ensure that the next switch is allowed to turn on only after the previous switch is completely turned off. Secondly, the narrow pulse phenomenon refers to short and sharp current or voltage fluctuations in the inverter output waveform. Such fluctuations will affect the output quality of the inverter and cause high-frequency harmonic components to appear in the spectrum.

[0030] Therefore, based on the above problems, the present application proposes an inverter modulation method, which sets two modulation modes without adding additional hardware, and selects between the two modulation modes according to the actual situation of the inverter, combining dead zone compensation and narrow pulse suppression, avoiding the situation where only one of the problems is adjusted, thereby aggravating the other problem, so as to increase the performance of the inverter under different working conditions and solve the problems caused by narrow pulse and dead zone effects.

[0031] The inverter modulation method provided in the present application comprises the following steps: Figure 1 As shown, the power parameters and environmental parameters of the inverter are obtained; according to the comparison results of the power parameters and environmental parameters with the set thresholds, the modulation mode of the inverter is selected. Among them, the modulation mode selection includes a first modulation mode and a second modulation mode, the first modulation mode is: adjusting the drive signal of the corresponding switch bridge arm of the inverter, and the second modulation mode is: setting the dead zone compensation time of the switch bridge arm.

[0032] According to the principles of the scheme of this application, in the modulation process of the inverter, power parameters and environmental parameters are important factors that determine the selection of the modulation mode. According to 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 is described in detail below. It is assumed that the inverter is connected to the power grid and is running. 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 commonly used models and can meet the use conditions, so they will not be described here.

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

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

[0036] It can be understood that after the modulation ratio m is obtained by 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 adopted for modulation. According to the calculation formula of the modulation ratio m, the bus voltage U on the DC side is dc The larger it is, the smaller the modulation ratio m is.

[0037] In this embodiment, Figure 3 As shown, the grid voltage U ac The lower the DC bus voltage U dc The higher the modulation ratio, the lower the modulation ratio m. When the modulation ratio m is low, the inverter will not generate narrow pulses. The reason is that in the process of frequency modulation, a low modulation ratio usually means a smaller frequency offset and the frequency change of the carrier will not be large. In other words, when the modulation ratio is low, the range of frequency offset is relatively small, the high-frequency part of the generated frequency spectrum is relatively small, and the spectrum is mainly concentrated in the lower frequency range. When the modulation ratio is low, the waveform of the signal generated by the frequency modulation in the time domain changes slowly, the pulse duration is longer, and a wide pulse is generated. Therefore, when the modulation ratio m is less than the modulation ratio threshold M, it is only necessary to adjust the drive signal of the corresponding bridge arm switch of the inverter.

[0038] Specifically, Figure 2 As shown, the inverter includes three groups of switch bridge arms, which correspond to the three phases of the power grid one by one. The switch bridge arms include a first power switch 110 and a second power switch 120 connected in series, wherein the first power switch 110 is connected to the positive end of the bus, and the second power switch 120 is connected to the negative end 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. When the inverter operates normally, the positive half cycle of the power grid actually requires the first transistor Q1 and the second diode D2 to output positive current; the negative half cycle of the power grid requires the first diode D1 and the second transistor Q2 to output.

[0039] It can be understood that when the inverter does not adopt the first modulation mode, the waveform of the inverter is as follows: Figure 4As shown, it is the error voltage waveform of the grid A phase output voltage and the dead zone effect, wherein 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 zone time t d , device turn-on delay t on and turn-off delay t off The driving waveform of V a * and V a is the ideal voltage and actual voltage of phase A; V err is the voltage error; T s is a carrier cycle; in an ideal state, the first power switch 110 is turned on while the second power switch 120 needs to be turned off, thereby obtaining the waveforms shown by GaH* and GaL*, but during the switching process, the first power switch 110 and the second power switch 120 produce a certain delay, thereby obtaining the waveforms shown by GaH1 and GaL1, therefore, V a * and V a There is a voltage loss V err .

[0040] When the inverter adopts the first modulation mode, when the grid is in the positive half cycle, the driving signal of the second diode D2 is canceled; when the grid is in the negative half cycle, the driving signal of the first diode D1 is canceled. According to the above operation, it can be obtained Figure 5 The waveform in the figure only takes the first power switch 110 as an example, V a * and V a There is no voltage loss between err The voltage is 0, which can illustrate that the first modulation mode provided in the present application can effectively eliminate voltage loss.

[0041] However, when the modulation ratio m is greater than the modulation ratio threshold M, many factors need to be considered. When other conditions remain unchanged, if the DC side bus voltage increases, the DC side duty cycle of the inverter is higher, the switch tube conduction loss is greater, and the system generates more heat, the system temperature of the inverter will increase. In other words, the change in temperature can feedback the specific situation of the DC side bus voltage. It can be seen that it is very necessary to analyze the change of the DC side bus voltage from the perspective of the inverter system temperature.

[0042] In this embodiment, a temperature sensor is provided on the inverter to obtain the system temperature t of the inverter, such as the temperature of the inverter heat sink or the ambient temperature. The system temperature t mainly reflects the operating temperature of the electronic components inside the inverter. The temperature change will affect the switching performance and modulation accuracy of the inverter.

[0043] The system temperature t is compared with the temperature threshold T to further determine the working state of the inverter. The maximum system temperature T of the inverter is max De-rating 80% as temperature threshold T, maximum system temperature T max The recommended values ​​given by the manufacturer based on factors such as the internal components, heat dissipation capacity, and environmental adaptability of the inverter can be obtained by consulting the technical specifications of the inverter, and will not be repeated here. When the system temperature t is less than the temperature threshold T, the bus voltage on the DC side of the inverter is raised to suppress the generation of narrow pulses; when the system temperature t is greater than the temperature threshold T, it means that the switching frequency of the power switch of the inverter is higher, and more heat is generated. The switching frequency of the power switch is closely related to the duty cycle. Therefore, it is very necessary to make a modulation selection judgment based on the duty cycle d of the inverter.

[0044] It can be understood that the duty cycle d is the ratio of the time the switch element is turned on to the time of the entire cycle in one 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 will be, causing the pulse to become longer. Therefore, the signal maintains a high level for a longer time in one cycle, and a wide pulse is generated instead of a narrow pulse. Therefore, when the duty cycle d is greater than the duty cycle threshold D, the first modulation mode is selected, and only the drive signal of the corresponding switch bridge arm of the inverter is adjusted.

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

[0046] It should be known 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 value of the duty cycle threshold D is preferably 0.2. That is to say, the on-time of the switching device accounts for 20% of a cycle. By setting the duty cycle d to a smaller value, the on-time of the switching element can be effectively reduced, thereby reducing the loss during the switching operation. At the same time, the switching device will experience greater thermal stress during a longer on-time. A shorter on-time can help reduce the heat accumulation of the switching device and reduce the risk of overheating, thereby extending the service life of the device.

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

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

[0049] In this embodiment, Figure 6 As shown, when the current i flowing through the switch bridge arm a When the voltage drop of the device itself is ignored and the control signal is an ideal driving signal, at time t0, the first power switch 110 is turned on and the second power switch 120 is turned off, and the voltage of phase A increases to V dc However, due to the dead time t d , the second power switch 120 is turned on with a delay, and the delay time is t on , the second power switch 120 is turned on at time t2. During the period from t1 to t2, the current passes through other paths in the circuit or reverse current exchange occurs, resulting in current loss. In an ideal state, at time t3, the first power switch 110 is turned off and the second power switch 120 is turned on, and the A phase voltage begins to drop. However, due to the turn-off delay t of the first power switch 110, off , causing the first power switch 110 to be turned off at time t4, which in turn causes the voltage to increase. a * and V a It can be seen from the waveform that voltage loss occurs.

[0050] From the above analysis, we can know that the voltage error caused by the dead time and the power switch delay can be calculated by the following formula: a >0, V 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 the second modulation mode is adopted, the dead time t d , conduction delay t on and disconnection delay t off , the dead zone compensation time t required to be compensatedcom The value of is obtained by the following calculation formula: a >0, t com =t d +t on- t off ; when i a When t com =t off -t d -t on , thus eliminating voltage loss.

[0052] The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and the specification only describe the principles of the present application. The present application may have various changes and improvements without departing from the spirit and scope of the present application, and these changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the attached claims and their equivalents.

Claims

1. An inverter modulation method, characterized in that: The steps include: Obtain the power parameters and environmental parameters of the inverter; Selecting a modulation mode of the inverter according to the comparison results of the power parameter and the environmental parameter with the set threshold values ​​respectively; The modulation mode includes a first modulation mode and a second modulation mode. The first modulation mode is: adjusting the driving signal of the switch bridge arm corresponding to the inverter, and the second modulation mode is: setting the dead zone compensation time of the switch bridge arm.

2. The inverter modulation method according to claim 1, characterized in that: The modulation mode selection of the inverter includes the following process: calculating the modulation ratio by the power parameter, and comparing the obtained modulation ratio with the 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 modulation selection of the inverter will continue to be judged in combination with the environmental parameters.

3. The inverter modulation method according to claim 2, characterized in that: The power parameters include the peak value U of the grid voltage on the AC side of the inverter ac_max And the DC bus voltage U dc ; The modulation ratio m is calculated as follows:

4. The inverter modulation method according to claim 3, characterized in that: The environmental parameter is the system temperature of the inverter; judging the modulation selection of the inverter based on the system temperature includes the following process: comparing the system temperature with a set temperature threshold; if the system temperature is lower than the temperature threshold, the inverter will select the first modulation mode for modulation; Otherwise, the modulation selection will be determined in combination with the duty cycle of the inverter.

5. The inverter modulation method according to claim 4, characterized in that: Before the system temperature is lower than the temperature threshold to control the inverter to adopt the first modulation mode for modulation, the DC side bus voltage of the inverter is first increased.

6. The inverter modulation method according to claim 4, characterized in that: Judging the modulation selection of the inverter based on the duty cycle includes the following process: calculating the duty cycle of the inverter in real time according to the power parameter and comparing it with the set duty cycle threshold; if the duty cycle is greater than the duty cycle threshold, the inverter will select the first modulation mode for modulation, otherwise select the second modulation mode for modulation.

7. The inverter modulation method according to claim 6, characterized in that: The duty cycle threshold is 0.

2.

8. The inverter modulation method according to claim 7, characterized in that: The calculation process of the modulation ratio threshold M is as follows: by given the duty cycle threshold D and the grid voltage U ac , calculate the first voltage value U of the DC side bus voltage dc0 ; The first voltage value U dc0 The calculation formula is as follows: dc0 =U ac *T on / T; The first voltage value U dc0 Substitute the modulation ratio m into the calculation formula for calculation, and record the obtained modulation ratio m as the modulation ratio threshold M.

9. The inverter modulation method according to any one of claims 1 to 7, characterized in that: The inverter is connected to a power grid, the switch bridge arm includes a first power switch and a second power switch connected in series, the first power switch is connected to a positive end of a bus, the second power switch is connected to a negative end 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 a positive half cycle, canceling the driving signal of the second diode D2; When the power grid is in a negative half cycle, the driving signal of the first diode D1 is canceled.

10. The inverter modulation method according to any one of claims 1 to 7, characterized in that: The electrical quantity parameters include the dead time, the on-delay and the off-delay of each switch device in the switch bridge arm; when controlling the inverter to perform the second modulation mode, the dead time compensation time is calculated according to the dead time, the on-delay and the off-delay; the modulation waveform is compensated by the dead time compensation time, thereby suppressing the voltage error caused by the dead time and the device action 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 zone compensation time is calculated as follows: com =t d +t on- t off ; When the current flowing through the switch bridge arm is less than 0, the dead zone compensation time is calculated as follows: com =t off -t d -t on ; Among them, t on is the turn-on delay, t d is the dead time, t off is the disconnection delay.

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