Inverter low-temperature cold start control method

Abstract

This application proposes a low-temperature cold start control method for an inverter, comprising: S1: powering on and detecting the ambient temperature; S2: determining whether the ambient temperature is lower than the low-temperature set value, and if so, proceeding to step S3; S3: applying a probe pulse PWM drive signal to the switching transistor in the inverter switching unit; S4: detecting and obtaining the instantaneous fluctuation value of the DC bus voltage and the peak value of the bus current flowing through the DC bus, and calculating the impedance characteristic factor of the electrolytic capacitor based on the instantaneous fluctuation value of the DC bus voltage and the peak value of the bus current; S5: obtaining the calibrated proportional coefficient and calibrated integral coefficient in the PID control loop based on the impedance characteristic factor; S6: the control unit outputs a switching control signal for controlling the switching transistor in the inverter switching unit based on the sampled value of the DC bus voltage, the calibrated proportional coefficient, and the calibrated integral coefficient, so that the inverter enters voltage closed-loop control.

Description

Technical Field

[0001] This application relates to the field of electronic technology, and in particular to a method for controlling the low-temperature cold start of an inverter. Background Technology

[0002] Inverters, as core equipment in power electronic systems, are widely used in photovoltaic power generation, energy storage, and motor drives. In extremely cold regions, inverters often need to start up in extremely low temperatures (such as below -25°C). The DC bus (BUS) side of the inverter is typically equipped with an electrolytic capacitor (Cbus) (such as an aluminum electrolytic capacitor Cbus) to provide voltage support and ripple smoothing. In extremely low temperatures, the viscosity of the electrolyte inside the electrolytic capacitor Cbus increases, leading to a significant increase in its equivalent series resistance. This deterioration of physical characteristics causes larger DC bus voltage ripple, directly affecting the stability of the inverter control loop.

[0003] To address the issue of starting up at extremely low temperatures, a conventional approach is to add external heating elements inside the inverter, relying on external heat conduction to raise the capacitor temperature. This method increases the system's hardware cost and structural complexity, and also results in a long heat transfer path and low heating efficiency. Another approach is to rely on the natural switching losses of the inverter's power devices for passive temperature rise. However, this method generates limited heat, and the capacitor temperature recovers slowly, causing the inverter to remain in derating or standby mode for too long, thus affecting the system's responsiveness.

[0004] To improve heating efficiency, existing technologies utilize inverter topology to generate alternating current, achieving active internal heating through the Joule heating effect of the equivalent series resistance of the electrolytic capacitor Cbus. However, in practical engineering applications, this active heating control strategy still has significant technical shortcomings. Under extremely low temperature and high impedance conditions, injecting ripple current into the DC bus BUS can easily cause large fluctuations in bus voltage. Due to the lack of effective decoupling and adaptive parameter adjustment mechanisms for the AC / DC control loop, the open-loop gain of the voltage control loop will shift due to increased impedance, leading to low-frequency oscillations in the system. This can easily trigger hardware overvoltage or undervoltage protection mechanisms, causing shutdown. Furthermore, existing active heating schemes typically use current injection with fixed amplitude and frequency, which can easily induce structural resonance in magnetic components, generating acoustic howling, and lack closed-loop constraints on the internal temperature rise gradient of the capacitor. In cases where the capacitor exhibits parameter dispersion or aging, unconstrained current injection can easily lead to excessively rapid localized heating, posing a safety hazard of thermal runaway. Summary of the Invention

[0005] According to one embodiment, this application provides a low-temperature cold start control method for an inverter. The inverter includes an inverter switching unit and a control unit. An electrolytic capacitor is connected to the DC bus side of the inverter switching unit. The control unit is used to control the switching transistors within the inverter switching unit, including: S1: Powering on and detecting the ambient temperature. S2: Determine ambient temperature Is it lower than the low temperature set value? If so, proceed to step S3; S3: Apply a probe pulse PWM drive signal to the switching transistor in the inverter switching unit; S4: Detect and obtain the instantaneous fluctuation value of the DC bus voltage. and the peak bus current flowing through the DC bus According to the instantaneous fluctuation value of the DC bus voltage and the peak value of the bus current Calculate the impedance characteristic factor of the electrolytic capacitor. S5: Based on the impedance characteristic factor Obtain the calibrated proportional coefficient in the PID control loop and calibrated integral coefficients S6: The control unit, based on the DC bus voltage sampling value and the calibrated proportional coefficient... and the calibrated integral coefficients The output controls the switching signal of the switching transistor in the inverter switching unit, so that the inverter enters voltage closed-loop control.

[0006] Furthermore, if step S2 determines otherwise, the inverter uses the standard proportional coefficient at room temperature. and standard integral coefficient Voltage closed-loop control is performed to start the inverter.

[0007] Furthermore, the duty cycle of the probe pulse PWM drive signal in step S3 is much smaller than the duty cycle required for normal inverter operation.

[0008] Furthermore, the duty cycle of the probe pulse PWM drive signal is between 1% and 2%.

[0009] Furthermore, in step S4, according to the formula... Calculate the impedance characteristic factor of the electrolytic capacitor. .

[0010] Furthermore, step S5 includes: S51: based on the impedance characteristic factor Obtain supplementary coefficients The supplementary coefficients mentioned above S52: Used to supplement the proportional and integral coefficients in the PID control loop; Based on the standard proportional coefficient at room temperature. Standard integral coefficient and the supplementary coefficient Obtain the calibrated proportional coefficient and calibrated integral coefficients .

[0011] Furthermore, in step S51, according to the formula... / Calculate the supplementary coefficient ,in This is the preset impedance compensation coefficient. This is the standard impedance characteristic factor at room temperature.

[0012] Furthermore, in step S52, according to the formula , The calibrated proportional coefficient is calculated and obtained. and the calibrated integral coefficients .

[0013] Furthermore, after step S6, the method further includes: S7: determining the instantaneous fluctuation value of the DC bus voltage. Has the value dropped below the set safety threshold? If so, proceed to step S8; S8: Make the proportional coefficient and integral coefficient in the PID control loop change from the calibrated proportional coefficient. and the calibrated integral coefficients Smooth transition to standard proportionality coefficient at room temperature and standard integral coefficient .

[0014] Furthermore, in step S8, a first-order lag filter is used to adjust the proportional and integral coefficients in the PID control loop so that they are adjusted from the calibrated proportional coefficient. and the calibrated integral coefficients Transitioning to the standard scaling factor at room temperature with minute steps and standard integral coefficient .

[0015] Furthermore, if step S7 determines the result to be negative, then proceed to step S6.

[0016] The features and technical advantages of this disclosure have been outlined quite extensively above to facilitate a better understanding of the detailed description that follows. Additional features and advantages of this disclosure, which form the subject matter of the claims, will be described below. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily used as the basis for modifying or designing other structures or processes for achieving the same purpose as this disclosure. Those skilled in the art will also recognize that such equivalent structures do not depart from the spirit and scope of this disclosure as set forth in the appended claims. Attached Figure Description

[0017] To gain a more complete understanding of this disclosure and its advantages, the following description is given in conjunction with the accompanying drawings, wherein:

[0018] Figure 1 A typical inverter schematic diagram is shown;

[0019] Figure 2 A schematic flowchart of an inverter low-temperature cold start control method according to an embodiment of this application is shown;

[0020] Figure 3 A schematic flowchart of an inverter low-temperature cold start control method according to another embodiment of this application is shown;

[0021] Figure 4 This diagram shows a comparison curve of the startup voltage performance of the present invention and the prior art at a low temperature of -25°C.

[0022] Figure 5 A schematic flowchart of an inverter low-temperature cold start control method according to another embodiment of this application is shown.

[0023] Unless otherwise stated, corresponding numbers and symbols in the various figures generally refer to corresponding parts. These figures are drawn to clearly illustrate relevant aspects of the various embodiments and are not necessarily drawn to scale. Detailed Implementation

[0024] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] Please see Figure 1The schematic diagram of a typical inverter shown includes an inverter switching unit 110 and a control unit 120. An electrolytic capacitor Cbus is connected to the DC bus (BUS) side of the inverter switching unit 110, and its AC terminal is used to output AC (VAC). In actual implementation, a storage battery or solar cell can be connected to the DC bus (BUS) side of the inverter switching unit 110 to provide DC power to the DC bus (BUS). The inverter switching unit 110 includes a switching transistor, and the control unit 120 controls the switching transistor within the inverter switching unit 110 to switch between on and off states, thereby converting the DC power received on its DC bus (BUS) side into AC (VAC) power for supplying AC loads or grid connection.

[0026] The typical control method for existing inverters uses voltage outer-loop PID control, with a proportional coefficient... (Also known as standard proportional coefficient) and integral coefficient (Also known as the standard integral coefficient) is usually designed based on the parameters of the devices in the inverter at room temperature. For example, the capacitive reactance of the electrolytic capacitor Cbus is a low equivalent series resistance (ESR) at room temperature.

[0027] However, in extremely cold regions, inverters often need to start up in extremely low temperatures (such as below -25°C). At these temperatures, the electrolyte viscosity of the electrolytic capacitor Cbus on the DC bus increases, causing the equivalent series resistance (ESR) to rise exponentially, potentially reaching 5 to 10 times that at room temperature. If PID parameters at room temperature, i.e., the standard proportional coefficient, are still used in such conditions... and standard integral coefficient If control is applied, when a sharp increase in ESR is detected, the open-loop gain of the inverter will be too large and the phase margin will be reduced, thereby causing severe low-frequency voltage oscillations in the DC bus voltage. This not only leads to poor output power quality, but may also cause startup failure due to overvoltage, undervoltage or overcurrent protection. In severe cases, excessive ESR loss may cause the electrolytic capacitor to overheat and explode or burn out the switching transistor in the inverter switching unit 110.

[0028] Based on this, one embodiment of this application proposes a low-temperature cold start control method for inverters, which can be found in [reference needed]. Figure 2 The schematic diagram shown is a flowchart of an inverter low-temperature cold start control method according to an embodiment of this application. The inverter low-temperature cold start control method proposed in this application includes:

[0029] S1: Power on, detect ambient temperature ;

[0030] S2: Determine ambient temperature Is it lower than the low temperature set value? If so, proceed to step S3.

[0031] S3: Apply a probe pulse PWM drive signal to the switching transistor in the inverter switching unit 110;

[0032] S4: Detect and obtain the instantaneous fluctuation value of DC bus voltage. And the peak bus current flowing through the DC bus BUS Based on the instantaneous fluctuation value of DC bus voltage and peak bus current Calculate the impedance characteristic factor of electrolytic capacitor Cbus. ;

[0033] S5: Based on impedance characteristic factor Obtain the calibrated proportional coefficient in the PID control loop and calibrated integral coefficients ;

[0034] S6: Control unit 120 samples the DC bus voltage value. calibrated proportional coefficient and calibrated integral coefficients The output controls the switching signal of the switching transistor in the inverter switching unit 110, enabling the inverter to enter voltage closed-loop control.

[0035] For inverters, the ambient temperature detected by the temperature sensor is an indirect reflection. The sensor measures the temperature of the inverter casing or heat sink, while the internal ESR is determined by the core temperature of the electrolytic capacitor Cbus, and the two have different thermal time constants. The on-resistance of the switching transistor in the inverter switching unit 110 decreases at low temperatures, which is good for the inverter system. Furthermore, the switching transistor will not cause loop oscillation, but will only affect efficiency. The inductance value inside the inverter decreases at low temperatures, but at -40°C, the inductance value usually only decreases by 10%-20%, which is much smaller than the 10-50 times change in ESR, and the change in inductance does not directly cause loop oscillation.

[0036] The above analysis shows that the parameter changes of other components are either benign (e.g., the on-resistance of the switching transistor decreases at low temperatures) or the magnitude of the changes does not affect stability. The exponential increase in the ESR of the electrolytic capacitor Cbus is the only key parameter that causes the control loop to change from stable to unstable.

[0037] Therefore, this application correlates the "deterioration problem" of the dramatic increase in ESR of electrolytic capacitor Cbus at low temperatures with the proportional and integral coefficients of the control loop, and discovers the impedance characteristic factor of electrolytic capacitor Cbus. The degree of ESR "deterioration" can be quantified, thus allowing the impedance characteristic factor of the electrolytic capacitor Cbus to be determined. This is transformed into the basis for adjusting the proportional and integral coefficients, that is, based on the impedance characteristic factor of the electrolytic capacitor Cbus, which quantifies the degree of "deterioration" in ESR. The proportional gain of the PID control loop required for adaptive calibration and integral coefficient To ensure the stability of the loop.

[0038] It is evident that by selecting to monitor the dynamic performance of the electrolytic capacitor Cbus on the DC bus BUS, this application essentially eliminates the source of loop instability in the system under severe cold conditions, thereby achieving higher control precision.

[0039] In another embodiment of the actual implementation, see [reference needed]. Figure 3 The schematic diagram of the inverter low-temperature cold start control method according to another embodiment of this application is shown. If the determination in step S2 is negative, that is, the ambient temperature... If the inverter is not lower than the low-temperature setpoint, meaning it is in a non-extremely low-temperature environment (e.g., below -25°C), then proceed to step S9, where the inverter uses PID parameters at room temperature, i.e., the standard proportional coefficient. and standard integral coefficient Voltage closed-loop control is performed to start the inverter.

[0040] In one embodiment, the low temperature setting is -25°C. Of course, it can be adjusted according to actual needs, and this application does not limit it.

[0041] In one practical embodiment, the duty cycle of the probe pulse PWM drive signal in step S3 is much smaller than the duty cycle required for normal inverter operation. In a specific embodiment, the duty cycle of the probe pulse PWM drive signal is between 1% and 2% (e.g., 0.015). That is, when a non-destructive disturbance excitation is applied to the switching transistor in the inverter switching unit 110, the inverter does not output power. It can be seen that the inverter does not enter the power output mode at this time, but is locked in the "low temperature probe mode".

[0042] Furthermore, in step S4, according to the formula... Calculate the impedance characteristic factor of electrolytic capacitor Cbus. It is understandable that the impedance characteristic factor of the electrolytic capacitor Cbus is... The ESR of electrolytic capacitor Cbus can represent the impedance characteristic factor of electrolytic capacitor Cbus. The ESR of electrolytic capacitor Cbus directly reflects the ambient temperature of electrolytic capacitor Cbus on the DC bus. This directly reflects the ambient temperature of the electrolytic capacitor Cbus on the DC bus. Furthermore, as described above, the instantaneous fluctuation value of the DC bus voltage... and the peak bus current flowing through the DC bus BUS The voltage and current detection circuits of the inverter can be used to obtain the data, meaning that no additional hardware circuitry is required in this application.

[0043] Furthermore, step S5 includes:

[0044] S51: Based on impedance characteristic factor Obtain supplementary coefficients The supplementary coefficients mentioned above Used to supplement the proportional and integral coefficients in the PID control loop;

[0045] S52: Based on the standard proportionality coefficient at room temperature Standard integral coefficient and supplementary coefficient Obtain the calibrated proportional coefficient and calibrated integral coefficients .

[0046] Specifically, in actual implementation, step S51 is based on the formula / Calculate the supplementary coefficient ,in This is the preset impedance compensation coefficient. This is the standard impedance characteristic factor at room temperature. Specifically, as described above, The instantaneous fluctuation value of the DC bus voltage obtained by detection at room temperature can be used as a basis. and the peak bus current flowing through the DC bus BUS According to the formula Obtained through calculation. Specifically, Since these are constants obtained based on experience, this application does not limit their specific values.

[0047] Specifically, in actual implementation, step S52 is based on the formula , Calculate the calibrated proportional coefficient and calibrated integral coefficients .

[0048] Therefore, this application no longer attempts to blindly combat low temperatures, but instead utilizes the system's own sampling circuit and control loop to dynamically sense the ESR dynamic characteristics of the electrolytic capacitor Cbus, and based on the impedance characteristic factor of the electrolytic capacitor Cbus... The proportional and integral coefficients in the PID control loop are adjusted in real time and adaptively to offset the phase lag caused by the surge in ESR of the electrolytic capacitor Cbus, ensuring that the loop has sufficient stability margin at startup and ensuring reliable cold start of the inverter at low temperatures.

[0049] Please see Figure 4 The diagram shows a comparison of the startup voltage performance of the present invention and existing technologies at a low temperature of -25°C. The X-axis represents time (s), the Y-axis represents the DC bus voltage (V), and the target voltage is 400V. Curve A (gray dashed line) illustrates the hidden problem of the existing technology at extremely low temperatures due to the surge in ESR of the electrolytic capacitor Cbus. It shows severe low-frequency voltage oscillations after startup, with amplitudes exceeding 100V, potentially triggering hardware protection or causing capacitor damage. Curve B (thick black solid line) demonstrates the superiority of the present invention at extremely low temperatures. Although the "low-temperature detection mode" leads to "low-gain startup," resulting in a slightly slower initial voltage rise (i.e., "slow heating"), the bus voltage rises smoothly and monotonically to the target point of 400V without oscillations due to the compensation of the proportional and integral coefficients. The ripple is extremely small, protecting the electrolytic capacitor Cbus from large ripple overheating damage, achieving a highly stable and safe soft-start, and significantly extending the inverter's system lifespan.

[0050] It is evident that the technical solution provided in this application can eliminate the DC bus voltage oscillation caused by the surge in ESR of the electrolytic capacitor Cbus through pure software algorithm optimization without increasing any hardware costs. This ensures that the inverter can start smoothly and safely in extremely low temperature environments, with high reliability and significant cost advantages.

[0051] For further details, please refer to... Figure 5 The schematic diagram shown below illustrates another embodiment of the inverter low-temperature cold start control method of this application. The inverter low-temperature cold start control method proposed in this application further includes the following after step S6:

[0052] S7: Determine the instantaneous fluctuation value of DC bus voltage Has the temperature dropped below the set safety threshold? If so, proceed to step S8.

[0053] S8: This sets the proportional and integral coefficients in the PID control loop from the calibrated proportional coefficient... and calibrated integral coefficients Smooth transition to standard proportionality coefficient at room temperature and standard integral coefficient .

[0054] In practical applications, after a successful cold start of the inverter, the temperature of internal components gradually rises due to the inverter's own switching and inductor losses, and the capacitor ESR gradually decreases. Therefore, the instantaneous fluctuation value of the DC bus voltage... It also declined.

[0055] In practical implementation, in step S8, a first-order lag filter is used to adjust the proportional and integral coefficients in the PID control loop from the calibrated proportional coefficient. and calibrated integral coefficients Transitioning to the standard scaling factor at room temperature with minute steps and standard integral coefficient Specifically, the fine step size corresponding to the scaling factor is based on the calibrated scaling factor. Compared with the standard proportionality coefficient The difference between them is determined, for example, 5% of the difference; the fine step size corresponding to the integral coefficient is based on the calibrated integral coefficient. With standard integral coefficient The value is determined by the difference between them, for example, 5% of the difference.

[0056] Please refer to the following: Figure 5 If step S7 determines otherwise, then proceed to step S6, that is, continue to maintain the control unit based on the DC bus voltage sampling value and the calibrated proportional coefficient. and the calibrated integral coefficients The output controls the switching signal of the switching transistor in the inverter switching unit, so that the inverter enters voltage closed-loop control.

[0057] It is evident that this application can also achieve a smooth transition from "reliable low-temperature start-up" to "rated operation at room temperature after temperature rise".

[0058] Although embodiments of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the present disclosure as defined by the appended claims.

[0059] Furthermore, the scope of this application is not intended to be limited to the specific embodiments of the processes, machines, manufactures, compositions of matter, apparatuses, methods, and steps described in the specification. As will be readily understood by those skilled in the art from the disclosure of this publication, processes, machines, manufactures, compositions of matter, means, methods, or steps that perform substantially the same function, currently exist or will be developed or implemented thereafter, will yield substantially the same results as the corresponding embodiments described herein that are available according to this disclosure. Therefore, the appended claims are intended to include such processes, machines, manufactures, compositions of matter, apparatuses, methods, or steps within their scope.

Claims

1. A method for controlling the low-temperature cold start of an inverter, the inverter comprising an inverter switching unit and a control unit, wherein an electrolytic capacitor is connected to the DC bus side of the inverter switching unit, and the control unit is used to control the switching transistors within the inverter switching unit, characterized in that, include: S1: Power on, detect ambient temperature ; S2: Determine ambient temperature Is it lower than the low temperature set value? If so, proceed to step S3. S3: Apply a probe pulse PWM drive signal to the switching transistor in the inverter switching unit; S4: Detect and obtain the instantaneous fluctuation value of DC bus voltage. and the peak bus current flowing through the DC bus According to the instantaneous fluctuation value of the DC bus voltage and the peak value of the bus current Calculate the impedance characteristic factor of the electrolytic capacitor. ; S5: Based on the impedance characteristic factor Obtain the calibrated proportional coefficient in the PID control loop and calibrated integral coefficients ; S6: The control unit, based on the DC bus voltage sampling value and the calibrated proportional coefficient... and the calibrated integral coefficients The output controls the switching signal of the switching transistor in the inverter switching unit, so that the inverter enters voltage closed-loop control.

2. The inverter low-temperature cold start control method according to claim 1, characterized in that, If step S2 determines otherwise, the inverter uses the standard proportional coefficient at room temperature. and standard integral coefficient Voltage closed-loop control is performed to start the inverter.

3. The inverter low-temperature cold start control method according to claim 1, characterized in that, The duty cycle of the probe pulse PWM drive signal in step S3 is much smaller than the duty cycle required for normal operation of the inverter.

4. The inverter low-temperature cold start control method according to claim 3, characterized in that, The duty cycle of the probe pulse PWM drive signal is between 1% and 2%.

5. The inverter low-temperature cold start control method according to claim 1, characterized in that, In step S4, according to the formula Calculate the impedance characteristic factor of the electrolytic capacitor. .

6. The inverter low-temperature cold start control method according to claim 1, characterized in that, Step S5 includes: S51: Based on the impedance characteristic factor Obtain supplementary coefficients The supplementary coefficients mentioned above Used to supplement the proportional and integral coefficients in the PID control loop; S52: Based on the standard proportionality coefficient at room temperature Standard integral coefficient and the supplementary coefficient Obtain the calibrated proportional coefficient and calibrated integral coefficients .

7. The inverter low-temperature cold start control method according to claim 6, characterized in that, In step S51, according to the formula / Calculate the supplementary coefficient ,in This is the preset impedance compensation coefficient. This is the standard impedance characteristic factor at room temperature.

8. The inverter low-temperature cold start control method according to claim 6, characterized in that, In step S52, according to the formula , The calibrated proportional coefficient is calculated and obtained. and the calibrated integral coefficients .

9. The inverter low-temperature cold start control method according to claim 1, characterized in that, The process after step S6 also includes: S7: Determine the instantaneous fluctuation value of the DC bus voltage. Has the temperature dropped below the set safety threshold? If so, proceed to step S8. S8: This causes the proportional and integral coefficients in the PID control loop to change from the calibrated proportional coefficient... and the calibrated integral coefficients Smooth transition to standard proportionality coefficient at room temperature and standard integral coefficient .

10. The inverter low-temperature cold start control method according to claim 9, characterized in that, In step S8, a first-order lag filter is used to adjust the proportional and integral coefficients in the PID control loop from the calibrated proportional coefficient. and the calibrated integral coefficients Transitioning to the standard scaling factor at room temperature with minute steps and standard integral coefficient .

11. The inverter low-temperature cold start control method according to claim 9, characterized in that, If step S7 determines the result as negative, proceed to step S6.

Images