A single-phase grid-connected inverter TCM soft switching control method and system without inductance current zero-crossing detection

Abstract

The present application relates to the technical field of power electronic converter control, and discloses a single-phase grid-connected inverter TCM soft switching control method and system without inductance current zero-crossing detection. In view of the problems of existing TCM control, such as dependence on high-frequency inductance current sampling or zero-crossing detection, complex sampling circuit, hardware delay and noise interference affecting soft switching stability, the present application collects output current, DC bus voltage and grid voltage, determines the positive peak value of inductance current according to reference current and preset negative current, calculates the conduction time, turn-off time and switching period of the current switching period, and updates the PWM period and comparison value accordingly to generate the PWM driving signal of the full-bridge inverter bridge. The method can realize TCM soft switching operation without detecting the zero-crossing point of inductance current, and is suitable for high-frequency and high-efficiency control of single-phase grid-connected inverters.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter control technology, and in particular to a TCM soft-switching control method and system for a single-phase grid-connected inverter without inductor current zero-crossing detection. Background Technology

[0002] With the development of distributed photovoltaic power generation and high-power-density power supplies, single-phase grid-connected inverters are facing higher demands for efficiency and high switching frequency. TCM control, by causing the filter inductor current to flow in reverse during each switching cycle, provides the conditions for zero-voltage turn-on of the full-bridge inverter bridge switching devices, thereby reducing switching losses. Existing TCM control methods typically rely on inductor current zero-crossing detection signals or cycle-by-cycle high-frequency inductor current sampling to determine the switching state transition time. However, under high-frequency operating conditions, zero-crossing detection and high-frequency sampling circuits are easily affected by sampling bandwidth, hardware delay, noise interference, and parasitic parameters, leading to complex detection circuits and reduced control reliability. Therefore, a single-phase grid-connected inverter TCM soft-switching control method and system that does not rely on inductor current zero-crossing detection signals as the switching state transition trigger condition is needed. Summary of the Invention

[0003] The purpose of this invention is to provide a soft-switching control method and system for a single-phase grid-connected inverter TCM without inductor current zero-crossing detection, which solves the problems of existing TCM control relying on inductor current zero-crossing detection or high-frequency inductor current sampling, resulting in complex sampling circuits, significant hardware delay effects, noise sensitivity, and high control implementation costs.

[0004] To achieve the above objectives, this invention provides a TCM soft-switching control method for a single-phase grid-connected inverter without inductor current zero-crossing detection. The single-phase grid-connected inverter includes a DC bus, a full-bridge inverter bridge, a filter inductor, and an output filter unit. The method does not use the inductor current zero-crossing detection signal as the trigger condition for the switching state of the full-bridge inverter bridge, and includes the following steps:

[0005] Step 1: Collect the output current, DC bus voltage, and grid voltage of the single-phase grid-connected inverter; determine the positive peak value of the inductor current based on the reference current and the preset negative current, wherein the preset negative current is used to cause the inductor current to flow in reverse during the switching cycle.

[0006] Step 2: Calculate the on-time, off-time, and switching cycle of the current switching cycle based on the positive peak value of the inductor current, the preset negative current, the DC bus voltage, and the grid voltage.

[0007] Step 3: Update the PWM period and PWM comparison value according to the conduction time and switching period, and generate the PWM drive signal of the full-bridge inverter bridge, so that the single-phase grid-connected inverter can operate in TCM soft-switching mode without detecting the zero-crossing point of the inductor current.

[0008] Furthermore, in step one, the output current is acquired at a fixed sampling frequency lower than the inverter switching frequency, and the output current is used to characterize the low-frequency component of the grid-connected current or the filter inductor current.

[0009] Furthermore, the preset negative current is preset according to the reverse current margin required for the zero-voltage turn-on of the switching device, so as to cause the inductor current to flow in reverse during the switching cycle.

[0010] Furthermore, the positive peak value of the inductor current is determined based on the reference current and the preset negative current, so that the average value of the inductor current within one switching cycle follows the reference current.

[0011] Furthermore, the on-time is calculated based on the process of the inductor current rising from the negative peak corresponding to the preset negative current to the positive peak of the inductor current, and the off-time is calculated based on the process of the inductor current falling from the positive peak of the inductor current to the negative peak corresponding to the preset negative current. The switching cycle is determined by the on-time and off-time.

[0012] Furthermore, the PWM counting period is updated according to the switching period, and the PWM comparison value is updated according to the conduction time to generate a frequency conversion PWM drive signal.

[0013] This invention also provides a single-phase grid-connected inverter TCM soft-switching control system without inductor current zero-crossing detection, used to execute the above control method. The control system includes a sampling module, a peak value determination module, a switching cycle calculation module, and a PWM generation module. The sampling module is used to collect the output current, DC bus voltage, and grid voltage. The peak value determination module is used to determine the positive peak value of the inductor current based on the reference current and a preset negative current. The switching cycle calculation module is used to calculate the on-time, off-time, and switching cycle. The PWM generation module is used to generate the PWM drive signal for the full-bridge inverter bridge.

[0014] Compared with existing technologies, this invention does not use the inductor current zero-crossing detection signal as the trigger condition for the switching state of the full-bridge inverter bridge. Instead, it determines the positive peak value of the inductor current based on the output current, DC bus voltage, and grid voltage, and calculates the conduction time, turn-off time, and switching cycle in conjunction with a preset negative current, thereby generating a frequency conversion PWM drive signal. Therefore, this invention reduces the reliance on cycle-by-cycle inductor current zero-crossing detection and high-frequency current sampling circuits, reduces the complexity of sampling and detection circuits, and provides soft-switching conditions for zero-voltage turn-on of switching devices through a preset negative current, making it suitable for TCM soft-switching control of single-phase grid-connected inverters. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the main circuit structure of a single-phase grid-connected inverter in an embodiment of the present invention.

[0017] Figure 2 This is a flowchart of the TCM soft-switching control method without inductor current zero-crossing detection in an embodiment of the present invention.

[0018] Figure 3 This is a waveform diagram showing the positive peak value of the inductor current, the preset negative current, the on-time, and the off-time in the TCM mode of this embodiment of the invention.

[0019] Figure 4 This is a block diagram of the TCM soft-switching control system without inductor current zero-crossing detection in an embodiment of the present invention.

[0020] Figure 5 This is a simulation waveform of the inductor current under TCM soft-switching control without inductor current zero-crossing detection in an embodiment of the present invention. Figure 5 (a) is the overall waveform of the inductor current. Figure 5 (b) is a magnified view of the inductor current. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the protection scope of the present invention.

[0022] like Figure 1As shown, the single-phase grid-connected inverter in this embodiment includes a DC bus, a DC-side electrolytic capacitor, a full-bridge inverter bridge, a filter inductor, and an output filter unit. In one embodiment, the output filter unit includes a filter capacitor C. f and grid-connected side inductor L m The full-bridge inverter bridge includes four switching transistors: S1, S2, S3, and S4. The single-phase grid-connected inverter collects the output current, DC bus voltage, and grid voltage, and generates the PWM drive signal for the full-bridge inverter bridge according to the method described in this embodiment.

[0023] The control method in this embodiment does not use the inductor current zero-crossing detection signal as the trigger condition for the switching state switching of the full-bridge inverter bridge. That is to say, in this embodiment, it is not necessary to detect whether the inductor current crosses zero in each switching cycle, nor is it necessary to use the inductor current zero-crossing signal as the trigger signal for PWM toggling or switching state switching.

[0024] like Figure 2 As shown in the figure, the TCM soft-switching control method for a single-phase grid-connected inverter without inductor current zero-crossing detection provided in this embodiment includes the following steps.

[0025] Step 1: Collect the output current, DC bus voltage, and grid voltage of the single-phase grid-connected inverter; determine the positive peak value of the inductor current based on the reference current and the preset negative current.

[0026] Specifically, the output current i is collected. o DC bus voltage V dc and grid voltage v o The output current i o The low-frequency components of the grid-connected current or filter inductor current are collected at a fixed sampling frequency lower than the inverter switching frequency.

[0027] Let the reference current be i ref The preset negative current amplitude is I. r , where I r >0. To induce reverse current flow during the switching cycle, the negative peak value of the inductor current is set to -I. r The positive peak value is I p When the reference current is positive, we can set:

[0028] At this time, the average value I of the inductor current during one switching cycle avg for:

[0029]

[0030] Therefore, the average inductor current can follow the reference current, and the inductor current has a negative component during the switching cycle, which provides the conditions for TCM soft switching operation.

[0031] When the reference current is negative, the above peak value relationship can be transformed according to the polarity of the reference current, so that the inductor current also flows in the reverse direction during the negative half-cycle. The above peak value calculation method is one implementation method. In other implementation methods, the positive peak value of the inductor current can also be determined according to the output current error, current control quantity, or table lookup method, as long as the average value of the inductor current within one switching cycle can follow the reference current.

[0032] Step 2: Calculate the on-time, off-time, and switching cycle of the current switching cycle based on the positive peak value of the inductor current, the preset negative current, the DC bus voltage, and the grid voltage.

[0033] Specifically, let the filter inductance be L. f If the change in current required for the inductor current to rise from the negative peak to the positive peak is ΔI, then:

[0034]

[0035] In one implementation, when the reference current is positive, because ,therefore:

[0036]

[0037] When the reference current is negative, the amplitude of the reference current can be used in the calculation, that is:

[0038]

[0039] Let the DC bus voltage be V. dc The grid voltage is v o In one implementation, the full-bridge inverter bridge employs bipolar modulation and uses the absolute value of the grid voltage in the calculation. Therefore, the inductor voltage during the rising phase of the inductor current can be expressed as:

[0040]

[0041] The inductor voltage during the decreasing phase of the inductor current can be expressed as:

[0042]

[0043] Based on the inductance volt-second relationship, the conduction time T on and shutdown time T off They are respectively:

[0044]

[0045] Current switching period T s for:

[0046]

[0047] Among them, T d This refers to dead time, drive delay, or equivalent delay time; when dead time and equivalent delay are ignored, Current switching frequency f s for:

[0048]

[0049] To avoid calculation errors, T can be adjusted. on T off and T s Set an upper or lower limit value. For example, when V dc -|v o When T is too small, the denominator is limited; when T is too small, the denominator is limited. on or T off When the pulse width is less than the minimum allowable pulse width, the minimum pulse width value is used for updating. This limiting process does not change the control principle of this invention, which does not use the inductor current zero-crossing detection signal as the trigger condition for switching state transition.

[0050] Step 3: Update the PWM period and PWM comparison value according to the conduction time and switching period, and generate the PWM drive signal for the full-bridge inverter bridge.

[0051] Specifically, based on the current switching period T s Determine the PWM period based on the conduction time T. on The PWM comparison value is determined, thereby generating the variable frequency PWM drive signal. The PWM duty cycle D can be expressed as:

[0052]

[0053] The PWM drive signal is used to drive the full-bridge inverter bridge, causing the filter inductor current to rise from a negative peak to a positive peak and then fall back to a negative peak within one switching cycle. Because the inductor current flows in reverse during the switching cycle, it can provide energy for charging and discharging the output capacitor of the switching device during the dead time, thus reducing the voltage across the switching device to be turned on, thereby creating conditions for zero-voltage turn-on.

[0054] like Figure 3 As shown, the inductor current has a positive peak value I during one switching cycle. p Preset negative current -I r On-time T on and shutdown time T offUnlike control methods based on inductor current zero-crossing detection, this embodiment does not detect the actual zero-crossing point of the inductor current, nor does it wait for the zero-crossing detection circuit to output a flip signal. Instead, it calculates the conduction time, turn-off time, and switching cycle based on the sampled quantities such as output current, DC bus voltage, and grid voltage, combined with a preset negative current, and then generates a PWM drive signal to enable the single-phase grid-connected inverter to operate in TCM soft-switching mode.

[0055] like Figure 4 As shown, this embodiment also provides a single-phase grid-connected inverter TCM soft-switching control system without inductor current zero-crossing detection, including a sampling module, a peak value determination module, a switching cycle calculation module, and a PWM generation module. The sampling module is used to collect the output current, DC bus voltage, and grid voltage; the peak value determination module is used to determine the positive peak value of the inductor current based on the reference current and a preset negative current; the switching cycle calculation module is used to calculate the on-time, off-time, and switching cycle based on the positive peak value of the inductor current, the preset negative current, the DC bus voltage, and the grid voltage; the PWM generation module is used to generate the PWM drive signal for the full-bridge inverter bridge based on the on-time and switching cycle.

[0056] like Figure 5 As shown, the TCM soft-switching control method without inductor current zero-crossing detection described in this embodiment is simulated and verified. Figure 5 (a) is the overall waveform of the inductor current. It can be seen that the inductor current changes with the power frequency cycle and forms a high-frequency triangular current waveform in each switching cycle. Figure 5 (b) is Figure 5 (a) shows the enlarged diagram of the inductor current during a local switching cycle. It can be seen that the inductor current drops from the positive current to near the preset negative current -Ir, and rises again without being triggered by the inductor current zero-crossing detection signal. This indicates that this embodiment can still make the inductor current flow in reverse during the switching cycle without detecting the inductor current zero-crossing point, thereby satisfying the reverse current condition required for TCM soft switching operation.

Claims

1. A soft-switching control method for a single-phase grid-connected inverter with TCM without inductor current zero-crossing detection, characterized in that, The single-phase grid-connected inverter includes a DC bus, a full-bridge inverter bridge, a filter inductor, and an output filter unit. The method does not use the inductor current zero-crossing detection signal as the trigger condition for the switching state of the full-bridge inverter bridge, and includes the following steps: Step 1: Collect the output current, DC bus voltage, and grid voltage of the single-phase grid-connected inverter; determine the positive peak value of the inductor current based on the reference current and the preset negative current, wherein the preset negative current is used to cause the inductor current to flow in reverse during the switching cycle. Step 2: Calculate the on-time, off-time, and switching cycle of the current switching cycle based on the positive peak value of the inductor current, the preset negative current, the DC bus voltage, and the grid voltage. Step 3: Update the PWM period and PWM comparison value according to the conduction time and switching period, and generate the PWM drive signal of the full-bridge inverter bridge, so that the single-phase grid-connected inverter can operate in TCM soft-switching mode without detecting the zero-crossing point of the inductor current.

2. The single-phase grid-connected inverter TCM soft-switching control method without inductor current zero-crossing detection according to claim 1, characterized in that, In step one, the output current is sampled at a fixed sampling frequency lower than the inverter switching frequency. The output current is used to characterize the low-frequency component of the grid-connected current or the filter inductor current, and the zero-crossing point of the inductor current in each switching cycle is not detected.

3. The single-phase grid-connected inverter TCM soft-switching control method without inductor current zero-crossing detection according to claim 1, characterized in that, In step one, the preset negative current is preset according to the reverse current margin required for the switching device to turn on at zero voltage.

4. The single-phase grid-connected inverter TCM soft-switching control method without inductor current zero-crossing detection according to claim 1, characterized in that, In step one, the positive peak value of the inductor current is determined based on the reference current and the preset negative current, so that the average value of the inductor current within one switching cycle follows the reference current.

5. The single-phase grid-connected inverter TCM soft-switching control method without inductor current zero-crossing detection according to claim 1, characterized in that, In step two, the on-time is calculated based on the current change required for the inductor current to rise from the negative peak corresponding to the preset negative current to the positive peak of the inductor current, and the off-time is calculated based on the current change required for the inductor current to fall from the positive peak of the inductor current to the negative peak corresponding to the preset negative current. The current switching cycle is obtained based on the on-time and off-time.

6. The single-phase grid-connected inverter TCM soft-switching control method without inductor current zero-crossing detection according to claim 1, characterized in that, In step three, the PWM counting period is updated according to the switching period, and the PWM comparison value is updated according to the conduction time to generate a frequency conversion PWM drive signal.

7. A single-phase grid-connected inverter TCM soft-switching control system without inductor current zero-crossing detection, characterized in that, For performing the control method according to any one of claims 1-6, comprising: The sampling module is used to collect the output current, DC bus voltage, and grid voltage of the single-phase grid-connected inverter. The peak value determination module is used to determine the positive peak value of the inductor current based on the reference current and the preset negative current; The switching cycle calculation module is used to calculate the on-time, off-time, and switching cycle based on the positive peak value of the inductor current, the preset negative current, the DC bus voltage, and the grid voltage. The PWM generation module is used to update the PWM period and PWM comparison value according to the conduction time and switching period, and to generate the PWM drive signal of the full-bridge inverter bridge.

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