A three-phase power factor correction circuit and its starting method

Abstract

This application relates to the field of power electronics, and in particular to a three-phase power factor correction circuit and its starting method. It includes a starting method for the three-phase power factor correction circuit, which involves real-time detection of the peak voltage of each phase of the three-phase AC input and the positive and negative bus voltages. When both the positive and negative bus voltages are greater than the peak voltage of the first phase minus a preset safety difference, a first relay is controlled to engage to achieve soft start. The MCU control unit adjusts the PWM drive signal to raise the positive and negative bus voltages to target values, continuously adjusting until both the positive and negative bus voltages are greater than the peak voltages of the second and third phases, at which point the second and third relays are controlled to engage. The application also includes a three-phase power factor correction circuit, comprising an AC input unit, a soft start unit, a relay unit, a PFC power unit, a bus energy storage unit, a voltage detection unit, and an MCU control unit. This application effectively reduces the inrush current during startup, ensures stable and synchronized bus voltage, and prevents relay damage due to high current surges.

Description

Technical Field

[0001] This application relates to the field of power electronics, and in particular to a three-phase power factor correction circuit and its starting method. Background Technology

[0002] In the field of power electronics, three-phase power factor correction (PFC) circuits are widely used. With the development of power systems and the increasing demands for power quality, three-phase PFC circuits play a crucial role in improving power factor and reducing harmonic pollution. They optimize the operating efficiency of power equipment, reduce energy loss, and are of great significance to the stable and efficient operation of the entire power system.

[0003] In traditional three-phase PFC startup, to protect the relays, the bus capacitor is typically pre-charged to a certain voltage before the relays are engaged, thus reducing the inrush current flowing through the relays. Specifically, after AC power is applied, the bus capacitor is charged through a soft-start resistor. When the difference between the bus capacitor voltage and the peak voltage of a certain phase AC phase is detected to be less than a certain value, the relay for that phase is engaged, thereby achieving a soft start. In traditional startup schemes, after the first phase relay engages, the relays for the other two phases engage simultaneously.

[0004] However, this traditional starting scheme has obvious drawbacks. In some cases, soft-start resistors may not be allowed in the second and third phases. Furthermore, when there are differences in the effective values ​​of the AC voltages of different phases, if the relays of the other two phases are simultaneously activated in the traditional way, the bus voltage may be much lower than the peak voltage of these two phases, resulting in a large current flowing through the relays and causing them to be damaged. Summary of the Invention

[0005] The purpose of this application is to prevent high current surges from damaging relays, and a three-phase power factor correction circuit and starting method are provided.

[0006] A startup method for a three-phase power factor correction circuit, the startup method comprising the following steps:

[0007] S1: Real-time detection of the peak voltage of the first phase, the peak voltage of the second phase, the peak voltage of the third phase, the positive bus voltage, and the negative bus voltage of the three-phase AC input;

[0008] S2: First, precharge the positive bus capacitor and the negative bus capacitor through the soft start resistor. After the precharge is completed, determine whether the positive bus voltage is greater than the peak voltage of the first phase minus the preset safety difference, and whether the negative bus voltage is greater than the peak voltage of the first phase minus the preset safety difference. If both conditions are met, control the first relay to activate.

[0009] S3: The MCU control unit adjusts the PWM drive signal to raise the positive bus voltage and the negative bus voltage to the target value;

[0010] S4: Continuously adjust the positive bus voltage and the negative bus voltage until both the positive bus voltage and the negative bus voltage are greater than the peak voltage of the second phase and both are greater than the peak voltage of the third phase, then control the second relay and the third relay to engage.

[0011] By adopting the above technical solution, the peak voltage of each phase of the three-phase AC input, as well as the positive and negative bus voltages, are detected in real time, enabling accurate acquisition of the circuit's voltage status information. The system determines whether the positive and negative bus voltages are greater than the first phase peak voltage minus a preset safety difference. When this condition is met, the first relay is controlled to engage. Simultaneously, a soft-start resistor is used to achieve soft starting, effectively preventing large current surges caused by excessive differences between the bus capacitor voltage and the AC input voltage during the initial startup phase, thus protecting the first relay from damage. Next, the MCU control unit adjusts the PWM drive signal to raise the positive and negative bus voltages to target values, avoiding excessive voltage differences and ensuring circuit stability and reliability. Finally, the positive and negative bus voltages are continuously adjusted until they are both greater than the peak voltages of the second and third phases before the second and third relays are controlled to engage. This prevents large current surges caused by significant differences between the bus voltage and the second and third-phase AC input voltages at the moment of engagement, further protecting the circuit, extending its lifespan, improving the safety and stability of the entire three-phase power factor correction circuit, and enabling more efficient and stable circuit operation.

[0012] Preferably, in step S1, “real-time detection of the peak voltage of the first phase, the peak voltage of the second phase, and the peak voltage of the third phase of the three-phase AC input” specifically involves collecting the instantaneous voltage of each phase in the three-phase AC input, continuously recording and updating the maximum instantaneous voltage of each phase, and determining the maximum instantaneous voltage of each phase as the peak voltage of the corresponding phase.

[0013] By employing the above technical solution, the instantaneous voltages of each phase in the three-phase AC input are collected separately, and the maximum instantaneous voltage of each phase is continuously recorded and updated. The maximum instantaneous voltage of each phase is then determined as the peak voltage of the corresponding phase. This real-time detection and dynamic updating method makes the monitoring of the peak voltage of each phase more accurate, providing a reliable and precise voltage data basis for subsequent operations such as determining relay engagement conditions and adjusting bus voltage in the startup process. Based on accurate peak voltage data, the safe startup of the circuit can be more reasonably guaranteed when controlling relay engagement, avoiding situations such as large current damage to relays due to excessive differences between the positive and negative bus voltages and the peak AC input voltage, thus improving the safety and stability of the three-phase power factor correction circuit startup. At the same time, it provides an accurate basis for the MCU control unit to generate PWM drive signals based on voltage status and dynamically adjust the positive and negative bus voltages of the bus energy storage unit, which helps to achieve precise control and adjustment of the bus voltage and improve the performance and reliability of the entire three-phase power factor correction circuit.

[0014] Preferably, the preset safety difference value in step S2 is V. safe ≥I K1−max ×(R1+Req); I K1−max R1 is the rated maximum allowable inrush current of the first relay, R1 is the soft-start resistor value, and Req is the equivalent series resistance of each capacitor in the circuit during the initial stage of circuit startup.

[0015] By adopting the above technical solution, the preset safety difference is controlled to V. safe ≥I K1−max ×(R1+Req). During the startup of the three-phase power factor correction circuit, it effectively prevents the first relay from experiencing excessive inrush current due to a large difference between the positive and negative bus voltages and the peak voltage of the first phase. The soft-start resistor R1, together with the equivalent series resistance Req of each capacitor in the circuit, works in conjunction with the rated maximum allowable inrush current I of the first relay. K1−max This ensures that when the positive bus voltage is greater than the peak voltage of the first phase minus the preset safety difference, and the negative bus voltage is greater than the peak voltage of the first phase minus the preset safety difference, the current passing through the first relay during its activation is within its rated allowable range. This greatly reduces the risk of the first relay being damaged due to excessive inrush current, ensures the stability and reliability of the three-phase power factor correction circuit during startup, extends the service life of the first relay, reduces the possibility of circuit failure due to relay damage, and improves the operating efficiency and safety of the entire circuit system.

[0016] Preferably, the premise for controlling the first relay to engage in step S2 is that the soft-start resistor has completed the pre-charging of the positive and negative bus capacitors, and the engagement operation is only performed when both the positive and negative bus voltages meet the condition of "greater than the peak voltage of the first phase minus the preset safety voltage".

[0017] By adopting the above technical solution, after the soft-start resistor has completed the pre-charging of the bus capacitor, the first relay is only controlled to engage when both the positive and negative bus voltages are greater than the peak voltage of the first phase minus the preset safety voltage, effectively achieving soft starting. This avoids engaging the first relay when the bus capacitor voltage is too low, preventing a large current surge to the first relay due to a significant voltage difference between the bus capacitor and the first phase AC input, thus protecting the first relay from damage. It also reduces the impact on other components in the circuit, ensuring the stability and reliability of the three-phase power factor correction circuit during startup, extending the service life of circuit components, and improving the overall circuit efficiency and safety.

[0018] Preferably, in step S3, "adjusting the PWM drive signal" specifically involves adjusting the pulse width and frequency of the PWM drive signal to control the conduction time and switching frequency of the switching transistor, thereby controlling the rise of the positive and negative bus voltages.

[0019] By employing the above technical solution, and adjusting the pulse width and frequency of the PWM drive signal to control the conduction time and switching frequency of the switching transistors, the rise of the positive and negative bus voltages can be precisely controlled. This control method allows the positive and negative bus voltages to rise steadily at a predetermined rate, avoiding adverse effects on the circuit caused by excessively fast or slow voltage rises, thus ensuring the stability of the bus voltages and providing strong support for the stable operation of the three-phase power factor correction circuit. Simultaneously, this precise control allows for flexible adjustment of the voltage rise according to the actual needs of the circuit, improving the circuit's adaptability and reliability under different operating conditions.

[0020] Preferably, the target value in step S3 is the maximum value between the second-phase peak voltage and the third-phase peak voltage, which is determined based on the values ​​of the second-phase peak voltage and the third-phase peak voltage detected in real time in step S1.

[0021] By adopting the above technical solution, the target value in step S3 is set to the maximum value between the second-phase peak voltage and the third-phase peak voltage. This target value is determined based on the maximum value of the second-phase peak voltage and the third-phase peak voltage detected in real time during step S1. This provides a clear and reasonable reference standard for the positive and negative bus voltages during their rise. Using the real-time detected values ​​of the second-phase and third-phase peak voltages as the basis for determining the target value ensures that it accurately reflects the actual voltage conditions of the second and third phases in the three-phase AC input, avoiding problems during subsequent relay engagement due to unreasonable target value settings. In this way, in the subsequent step S4, it can be more effectively ensured that the positive and negative bus voltages, after reaching the target value, remain stably higher than both the second-phase and third-phase peak voltages. This better avoids large currents generated at the moment of engagement due to significant differences between the bus voltage and the second and third-phase peak voltages when controlling the engagement of the second and third relays, thus effectively protecting the second and third relays from damage and improving the stability and reliability of the three-phase power factor correction circuit during startup.

[0022] Preferably, in step S4, when controlling the second and third relays to engage, it is necessary to ensure that the positive bus voltage and the negative bus voltage are both stable and greater than the peak voltage of the second phase and the peak voltage of the third phase, so as to avoid the large current generated at the moment of engagement due to the large difference between the bus voltage and the second and third relays, which could damage the second and third relays.

[0023] By adopting the above technical solution, in step S4, when the second and third relays are energized, it is strictly ensured that both the positive and negative bus voltages are stably greater than the peak voltage of the second phase and the peak voltage of the third phase. This technique effectively avoids the generation of large currents at the moment the second and third relays are energized due to a large difference between the bus voltage and the peak voltages of the second and third phases. Since large currents may cause irreversible damage to the second and third relays, this solution greatly reduces the possibility of large current generation by stabilizing the relationship between the bus voltage and the peak voltage, thus providing good protection for the second and third relays, extending their service life, improving the stability and reliability of the three-phase power factor correction circuit, and reducing circuit failures and maintenance costs caused by relay damage.

[0024] A three-phase power factor correction circuit, and a starting method for the three-phase power factor correction circuit, wherein the three-phase power factor correction circuit includes:

[0025] An AC input unit is used to connect to a three-phase AC voltage and filter the three-phase AC voltage to provide filtered AC input power to the three-phase power factor correction circuit.

[0026] The soft-start unit includes a soft-start resistor (R1). One end of the soft-start resistor (R1) is connected to the first phase (AC1) output terminal of the AC input unit, and the other end is connected to the bus energy storage unit. It is used to pre-charge the bus energy storage unit in the early stage of circuit startup to avoid inrush current.

[0027] The relay unit includes a first relay (K1), a second relay (K2), and a third relay (K3). The input terminal of the relay unit is connected to the output terminal of the AC input unit and is used to control the on / off connection between the AC input of the corresponding phase and the power circuit.

[0028] The PFC power unit, whose input terminal is connected to the output terminal of the relay unit, includes a switching assembly and PFC inductors (L1, L2, L3) corresponding to the three phases, for adjusting the magnitude of the bus voltage.

[0029] The bus energy storage unit includes a positive bus capacitor (C7) and a negative bus capacitor (C8), which are connected to the output terminal of the PFC power unit and are used to store electrical energy to maintain a stable positive and negative bus voltage.

[0030] The voltage detection unit is connected to the AC input unit and the bus energy storage unit respectively, and is used to collect the peak voltage (Vp1, Vp2, Vp3) of the three-phase AC input and the positive and negative bus voltage (V7, V8).

[0031] The MCU control unit, connected to the voltage detection unit, relay unit, and PFC power unit, is used to generate PWM drive signals based on the voltage parameters and control the on / off state of each relay.

[0032] By adopting the above technical solutions, the AC input unit can connect to and filter three-phase AC voltage, providing a stable AC input power supply for the three-phase power factor correction circuit and ensuring the normal operation of the circuit. The soft-start resistor in the soft-start unit pre-charges the bus energy storage unit during the initial circuit startup, effectively avoiding inrush current, protecting other components in the circuit, and extending their service life. The relay unit can precisely control the on / off connection between the corresponding phase's AC input and the power circuit, flexibly adjusting the circuit's operating state. The PFC power unit, with the help of switching components and PFC inductors, can adjust the bus voltage according to actual needs. The bus energy storage unit uses positive and negative bus capacitors to store electrical energy, maintaining stable positive and negative bus voltages and providing a continuous and stable power supply for the entire circuit. The voltage detection unit can accurately collect the peak voltage of the three-phase AC input and the electrical signals of the positive and negative bus voltages, and transmit them to the MCU control unit, enabling the MCU control unit to understand the circuit's voltage status in a timely manner. The MCU control unit can process and judge the voltage parameter electrical signals transmitted by the voltage detection unit, accurately control the on / off state of each relay in the relay unit according to the voltage status, and generate appropriate PWM drive signals. By adjusting the pulse width and frequency, it controls the conduction and cutoff of the switching components, realizes the dynamic adjustment of the positive and negative bus voltages of the bus energy storage unit, and ensures that the circuit can operate stably and efficiently under different operating conditions.

[0033] Preferably, the AC input unit includes a first phase AC voltage (AC1), a second phase AC voltage (AC2), and a third phase AC voltage (AC3), which are respectively set to the first relay (K1), the second relay (K2), and the third relay (K3) of the relay, and the default state of each relay is open.

[0034] By adopting the above technical solution, the AC input unit is divided into first-phase AC voltage, second-phase AC voltage, and third-phase AC voltage, with corresponding first, second, and third relays, each with a default open state. This configuration allows the three-phase power factor correction circuit to perform phase-by-phase control during startup. Under different voltage conditions, the relays of each phase are sequentially activated according to actual needs, avoiding the problem of high current generation and relay damage caused by simultaneous activation of relays due to voltage differences between phases in traditional startup methods. Specifically, during startup, the first phase can be soft-started and the first relay activated first. Then, based on the relationship between the bus voltage and the peak voltages of other phases, the second and third relays are strategically activated, effectively protecting the relays, improving the safety and stability of circuit startup, extending the service life of the relays, and ensuring the normal operation of the three-phase power factor correction circuit.

[0035] Preferably, the switching components of the PFC power unit include power switch transistor groups arranged corresponding to the three phases, and the PFC power unit also includes PFC inductors arranged corresponding to the three phases. One end of the PFC inductor is connected to the output terminal of the relay unit, and the other end is connected to the power switch transistor group of the corresponding phase.

[0036] By adopting the above technical solution, the switching components of the PFC power unit use power switching transistor groups corresponding to the three phases, in conjunction with PFC inductors corresponding to the three phases. One end of the PFC inductor is connected to the output terminal of the relay unit, and the other end is connected to the power switching transistor group of the corresponding phase, enabling precise regulation of the three-phase AC input. The power switching transistor group can be turned on and off according to the control of the PWM drive signal, thereby controlling the energy transfer of the PFC inductor, allowing the PFC inductor to effectively transfer electrical energy to the bus energy storage unit. This connection method and setting can improve the regulation capability of the three-phase power factor correction circuit on the bus voltage, making the bus voltage regulation more flexible and precise, ensuring that the positive and negative bus voltages can be stably maintained within a suitable range, thus ensuring the stable operation of the entire three-phase power factor correction circuit. At the same time, it can also improve the power factor of the circuit, reduce power loss, and improve the performance and efficiency of the circuit.

[0037] Preferably, each power switch group includes two power switch transistors connected in series between the positive bus capacitor and the negative bus capacitor, and the series connection node is connected to the PFC inductor of the corresponding phase; the gate of the power switch transistor is connected to the PWM drive signal output terminal of the MCU control unit, and its conduction and cutoff are controlled by the PWM drive signal to regulate the energy transfer of the PFC inductor to the bus energy storage unit.

[0038] By adopting the above technical solution, two power switching transistors are connected in series between the positive and negative bus capacitors, and the series connection node is connected to the corresponding phase's PFC inductor, a reasonable circuit topology can be constructed. Simultaneously, by connecting the gate of the power switching transistor to the PWM drive signal output terminal of the MCU control unit, and using the PWM drive signal to control the on / off state of the power switching transistor, the energy transfer from the PFC inductor to the bus energy storage unit can be precisely adjusted. This improves the energy conversion efficiency of the three-phase power factor correction circuit, ensures the stability of the positive and negative bus voltages, reduces voltage fluctuations and interference, thereby improving the overall circuit performance and reliability. It effectively avoids equipment damage and malfunctions caused by unreasonable energy transfer, ensuring the stable and efficient operation of the three-phase power factor correction circuit.

[0039] Preferably, the voltage detection unit includes five detection branches:

[0040] The first detection branch is connected to the input terminal of the first phase of the AC input unit and is used to collect the peak voltage of the first phase;

[0041] The second detection branch is connected to the input terminal of the second phase of the AC input unit and is used to collect the peak voltage of the second phase.

[0042] The third detection branch is connected to the input terminal of the third phase of the AC input unit and is used to collect the peak voltage of the third phase.

[0043] The fourth detection branch is connected to the positive bus capacitor of the bus energy storage unit and is used to collect the positive bus voltage;

[0044] The fifth detection branch is connected to the negative bus capacitor of the bus energy storage unit and is used to collect the negative bus voltage;

[0045] The output of each detection branch is connected to the signal input of the MCU control unit.

[0046] By adopting the above technical solution, the voltage detection unit is configured with first to fifth detection branches, which are respectively connected to each phase of the three-phase AC input and the positive and negative busbars of the busbar energy storage unit. This enables accurate acquisition of the peak voltage of each phase of the three-phase AC input and the voltages of the positive and negative busbars. Connecting the output terminals of each detection branch to the signal input terminals of the MCU control unit allows for timely transmission of the acquired voltage signals to the MCU control unit. Based on this accurate voltage data, the MCU control unit can precisely control the on / off state of each relay in the relay unit. Simultaneously, it can generate appropriate PWM drive signals according to the voltage state and send them to the PFC power unit, thereby dynamically adjusting the positive and negative busbar voltages of the busbar energy storage unit. This ensures that the three-phase power factor correction circuit can operate stably and efficiently under different voltage conditions, avoiding circuit failures caused by inaccurate voltage detection and improving the reliability and stability of the circuit.

[0047] In summary, this application includes at least one of the following beneficial technical effects:

[0048] 1. Real-time detection of peak voltage and bus voltage of three-phase AC input enables accurate control of relay engagement even when soft-start resistors for the second and third phases are missing, solving the starting strategy problem;

[0049] 2. The bus capacitor is pre-charged using a soft-start resistor. Once the voltage condition is met, the first relay is activated, reducing the inrush current of the first relay and preventing damage to it.

[0050] 3. Adjust the bus voltage to be greater than the peak voltage of the second and third phases before activating the second and third relays to prevent large current from being generated due to voltage difference and to protect the second and third relays. Attached Figure Description

[0051] Figure 1 This is a flowchart of a startup method for a three-phase power factor correction circuit according to an embodiment of this application.

[0052] Figure 2 This is a partial circuit structure diagram of a three-phase power factor correction circuit according to one embodiment of this application;

[0053] Explanation of reference numerals in the attached diagram: Vp1, peak voltage of the first phase; Vp2, peak voltage of the second phase; Vp3, peak voltage of the third phase;

[0054] V7, positive bus voltage; V8, negative bus voltage;

[0055] R1, soft-start resistor; R2, first sampling resistor; R3, second sampling resistor; R4, third sampling resistor; R5, fourth sampling resistor; R6, fifth sampling resistor;

[0056] C7, positive bus capacitor; C8, negative bus capacitor;

[0057] K1, First Relay; K2, Second Relay; K3, Third Relay;

[0058] AC1, first phase of AC input unit; AC2, second phase of AC input unit; AC3, third phase of AC input unit;

[0059] L1 is the inductor corresponding to the first phase of the three-phase AC input in the PFC power unit; L2 is the inductor corresponding to the second phase of the three-phase AC input in the PFC power unit; L3 is the inductor corresponding to the third phase of the three-phase AC input in the PFC power unit.

[0060] Q1, the first power switch of the first phase power switch group in the PFC power unit; Q2, the second power switch of the first phase power switch group in the PFC power unit; Q3, the first power switch of the second phase power switch group in the PFC power unit; Q4, the second power switch of the second phase power switch group in the PFC power unit; Q5, the first power switch of the third phase power switch group in the PFC power unit; Q6, the second power switch of the third phase power switch group in the PFC power unit. Detailed Implementation

[0061] This application mainly adopts a phased control scheme for relay engagement and bus voltage regulation. It is designed for scenarios where there are no soft-start resistors for the second and third phases, and only the first phase retains a soft-start resistor. This achieves the effect of avoiding damage to the relays due to large currents when the three-phase power factor correction circuit is started. The following is a more detailed description of this application in conjunction with the accompanying drawings.

[0062] In one embodiment, such as Figure 1 As shown, this application discloses a startup method for a three-phase power factor correction circuit. The startup method for a three-phase power factor correction circuit includes:

[0063] S1: Real-time detection of the peak voltage of the first phase, the peak voltage of the second phase, the peak voltage of the third phase, the positive bus voltage, and the negative bus voltage of the three-phase AC input;

[0064] S2: First, precharge the positive bus capacitor and the negative bus capacitor through the soft start resistor. After the precharge is completed, determine whether the positive bus voltage is greater than the peak voltage of the first phase minus the preset safety difference, and whether the negative bus voltage is greater than the peak voltage of the first phase minus the preset safety difference. If both conditions are met, control the first relay to activate.

[0065] S3: The MCU control unit adjusts the PWM drive signal to raise the positive bus voltage and the negative bus voltage to the target value;

[0066] S4: Continuously adjust the positive bus voltage and the negative bus voltage until both the positive bus voltage and the negative bus voltage are greater than the peak voltage of the second phase and both are greater than the peak voltage of the third phase, then control the second relay and the third relay to engage.

[0067] Specifically, the real-time voltage detection step requires the use of a voltage detection device. For example, a high-precision voltage sensor can be used. This type of sensor typically employs the Hall effect principle, enabling it to quickly and accurately acquire the peak voltages of the first phase (Vp1), second phase (Vp2), third phase (Vp3), positive bus voltage (V7), and negative bus voltage (V8) of the three-phase AC input. Hall voltage sensors are characterized by good linearity, fast response speed, and adaptability to voltage signals of different frequencies and amplitudes. Alternatively, integrated voltage detection chips can be used. These chips offer advantages such as small size and high integration, allowing for easy installation in circuits for voltage detection. For instance, some integrated voltage detection chips utilize advanced CMOS technology, resulting in low power consumption and strong anti-interference capabilities. These detection devices then transmit the acquired voltage signals to the subsequent control unit.

[0068] In the pre-charging and judgment steps, the soft-start resistor R1 plays a crucial role. The soft-start resistor R1 is generally a resistive element with a certain resistance value, and its material can be made of alloy resistance wire. This material has good resistance stability and a low temperature coefficient, allowing it to maintain a relatively stable resistance value under different ambient temperatures. During the initial circuit startup, after the first phase AC1 of the AC input is powered on, the current flows through the soft-start resistor R1 to pre-charge the positive bus capacitor C7 and the negative bus capacitor C8. After pre-charging is complete, the control unit will determine whether the positive bus voltage V7 is greater than the first phase peak voltage Vp1 minus a preset safety difference, and whether the negative bus voltage V8 is greater than the first phase peak voltage Vp1 minus the preset safety difference. The preset safety difference needs to be determined based on the actual situation, and the formula is V... safe ≥I K1−max ×(R1+Req), where I K1−ma R1 is the rated maximum allowable inrush current of the first relay K1, R1 is the soft-start resistor value, and Req is the equivalent series resistance of all capacitors in the circuit during the initial startup phase. The first relay K1 will only be activated when both conditions are met. In practical applications, if the preset safety difference is set too small, the relay may activate before the bus voltage reaches the safe range, resulting in a large inrush current; if set too large, it will prolong the startup time and affect the circuit's efficiency.

[0069] The MCU control unit is the core control component of the entire circuit, adjusting the bus voltage. It utilizes a high-performance microcontroller chip, such as an ARM-based microcontroller, possessing powerful computing and control capabilities. The MCU control unit raises the positive bus voltage V7 and negative bus voltage V8 to target values ​​by adjusting the PWM drive signal. Specifically, this adjustment is achieved by modifying the pulse width and frequency of the PWM drive signal, controlling the on-time and switching frequency of the switching transistors, thereby controlling the rise of the positive and negative bus voltages V7 and V8. For example, when a higher bus voltage is needed, the MCU control unit increases the pulse width of the PWM drive signal, lengthening the on-time of the switching transistors, thus allowing more energy to be transferred to the bus capacitors, achieving a voltage increase. The target value here is the maximum of the second-phase peak voltage Vp2 and the third-phase peak voltage Vp3. During the adjustment process, the MCU control unit continuously makes dynamic adjustments based on the voltage feedback from the voltage detection unit to ensure that the bus voltage accurately reaches the target value.

[0070] The continuous adjustment of the bus voltage and the activation of the relays involves the MCU control unit continuously monitoring the voltage values ​​during the adjustment of the positive bus voltage V7 and the negative bus voltage V8. The second and third relays K2 will only activate when both V7 and V8 are greater than the second-phase peak voltage Vp2 and both are greater than the third-phase peak voltage Vp3, and when these voltages have stabilized at this state. This is to prevent large currents from being generated at the moment of activation due to significant differences between the bus voltage and the second-phase and third-phase peak voltages Vp2 and Vp3, which could damage the second and third relays K2 and K3. To ensure voltage stability, the MCU control unit can set a stabilization time threshold. The voltage is considered stable only when the conditions are met within this threshold time.

[0071] In practical industrial applications, such as the power systems of large factories, the stable startup of three-phase power factor correction circuits is crucial. Assume that in the factory's three-phase AC input, the first phase voltage has an effective value of 220V and a peak value of 311V, while the second and third phase voltages have an effective value of 270V and a peak value of 382V. According to traditional startup methods, if the bus voltage only reaches the first phase's peak voltage of 311V before activating the relays for the second and third phases, the large current generated will damage the relays because the bus voltage is much lower than the peak voltage of the second and third phases (382V). However, the startup method in this embodiment detects the voltage in real time, pre-charges the bus capacitor through a soft-start resistor, and activates the first relay when both the positive and negative bus voltages are greater than the first phase's peak voltage minus a preset safety difference. Then, the MCU control unit adjusts the bus voltage to be greater than the peak voltages of the second and third phases, and finally, after stabilization, activates the second and third relays. This effectively avoids damage to the relays from large currents and ensures the stable operation of the factory's power system.

[0072] Meanwhile, different industrial environments may present different interference factors. For example, in environments with strong electromagnetic interference, the accuracy of voltage detection may be affected. In such cases, optimization of the voltage detection device is necessary. A shielding layer can be added to the Hall voltage sensor or integrated voltage detection chip to reduce the impact of electromagnetic interference on the detection signal. Alternatively, digital filtering algorithms can be used to process the acquired voltage signal, remove interference signals, and improve detection accuracy.

[0073] When selecting a soft-start resistor, in addition to considering its resistance value and material, its power rating also needs to be taken into account. If the power rating is too low, the soft-start resistor may be damaged due to excessive heat during the pre-charging process. For example, in a high-power three-phase power factor correction circuit, the power rating of the soft-start resistor needs to be reasonably selected based on factors such as the total power of the circuit and the pre-charging time. The appropriate power value can be determined by calculating the power consumed by the soft-start resistor during the pre-charging process.

[0074] For the process of regulating the bus voltage by the MCU control unit, a PID control algorithm can also be used. The PID control algorithm can automatically adjust the pulse width and frequency of the PWM drive signal based on the error between the actual and target values ​​of the bus voltage, enabling the bus voltage to reach the target value more quickly and stably. Specifically, the proportional (P) stage can quickly adjust the output according to the magnitude of the error, the integral (I) stage can eliminate the steady-state error of the system, and the derivative (D) stage can predict the trend of error changes and make adjustments in advance. By properly setting the PID parameters, the regulation of the bus voltage can be made more precise and stable.

[0075] When determining whether the positive and negative bus voltages are stable, a method of multiple sampling and averaging can be used. For example, within a stable time threshold, the positive and negative bus voltages are sampled at regular intervals, and the average of the multiple sampled values ​​is calculated. If the average value fluctuates within a certain range, the voltage is considered stable. This method can reduce the impact of sampling errors on the judgment result and improve the accuracy of the judgment.

[0076] The implementation principle of this embodiment is as follows: This starting method charges the bus capacitor and engages the relay in stages, avoiding the need to engage the relay when the peak difference between the bus voltage and the AC voltage of each phase is large. This reduces the inrush current flowing through the relay and protects it. Real-time voltage detection and precise control based on voltage conditions improve the stability and safety of circuit startup, solving the problem of relay damage caused by differences in AC voltage between different phases in traditional starting schemes. This represents a significant improvement and contribution to existing technology. Through application in different industrial scenarios and optimized design of each component, the practicality and reliability of this starting method are further enhanced.

[0077] like Figure 2 As shown, a three-phase power factor correction circuit uses a three-phase power factor correction startup method. The three-phase power factor correction circuit includes:

[0078] An AC input unit is used to connect to a three-phase AC voltage and filter the three-phase AC voltage to provide filtered AC input power to the three-phase power factor correction circuit.

[0079] The soft-start unit includes a soft-start resistor R1. One end of the soft-start resistor R1 is connected to the first phase AC1 output terminal of the AC input unit, and the other end is connected to the bus energy storage unit. It is used to pre-charge the bus energy storage unit in the early stage of circuit startup to avoid inrush current.

[0080] The relay unit includes a first relay K1, a second relay K2, and a third relay K3. The input terminal of the relay unit is connected to the output terminal of the AC input unit and is used to control the on / off connection between the AC input of the corresponding phase and the power circuit.

[0081] The PFC power unit, whose input terminal is connected to the output terminal of the relay unit, includes a switching assembly and PFC inductors L1, L2, and L3 corresponding to the three phases, for adjusting the magnitude of the bus voltage.

[0082] The bus energy storage unit includes a positive bus capacitor C7 and a negative bus capacitor C8, which are connected to the output terminal of the PFC power unit to store electrical energy to maintain stable positive and negative bus voltages.

[0083] The voltage detection unit is connected to the AC input unit and the bus energy storage unit respectively, and is used to collect the peak voltages Vp1, Vp2, Vp3 of the three-phase AC input and the positive and negative bus voltages V7 and V8;

[0084] The MCU control unit, connected to the voltage detection unit, relay unit, and PFC power unit, is used to generate PWM drive signals based on the voltage parameters and control the on / off state of each relay.

[0085] Specifically, the AC input unit is used to input and filter the three-phase AC voltage. It includes phases AC1, AC2, and AC3, as well as input filter capacitors C1-C6. These input filter capacitors are typically ceramic capacitors, which have the advantages of stable capacitance and good high-frequency characteristics. These capacitors can filter out high-frequency interference signals in the three-phase AC voltage, providing a relatively clean AC input power supply for subsequent circuits. For example, ceramic capacitors can effectively bypass some high-frequency harmonic interference, thereby ensuring the quality of the input voltage.

[0086] In practical power systems, three-phase AC voltage can be affected by various factors, generating high-frequency harmonic interference. This harmonic interference not only affects the normal operation of subsequent circuits but may also damage power equipment. Ceramic capacitors have good high-frequency characteristics, maintaining a stable capacitance value over a wide frequency range and effectively filtering out high-frequency harmonics. However, the harmonic components and frequency ranges may differ for different power systems. Therefore, when selecting input filter capacitors, it is necessary to choose appropriate capacitance values ​​and types based on the actual situation. For example, in a power system containing many high-frequency harmonics, multiple ceramic capacitors with different capacitance values ​​can be combined to improve the filtering effect.

[0087] The soft-start resistor R1 in the soft-start unit, as mentioned earlier, is connected at one end to the first phase AC1 output terminal of the AC input unit and at the other end to the bus energy storage unit. During the initial circuit startup, the soft-start resistor R1 limits the current and pre-charges the bus energy storage unit, preventing inrush current from damaging the relays and other components. The resistance value of the soft-start resistor R1 needs to be selected by comprehensively considering factors such as circuit parameters and the rated current of the relays. If the resistance value is too large, the charging time will be too long; if the resistance value is too small, it will not effectively limit the inrush current. During the pre-charging process, the soft-start resistor consumes a certain amount of power and generates heat. Poor heat dissipation may lead to excessively high resistor temperatures, affecting its performance and lifespan. A heat sink can be installed on the soft-start resistor to increase the heat dissipation area and improve heat dissipation efficiency.

[0088] The relay unit includes a first relay K1, a second relay K2, and a third relay K3, corresponding to the first, second, and third phases of the three-phase AC input, respectively. The input terminals of each relay are connected to the output terminals of the AC input unit, and the default state of each relay is open. The relays are generally electromagnetic relays, which control the opening and closing of contacts through electromagnetic force, featuring rapid action and high reliability. When the coil of an electromagnetic relay is energized, it generates a magnetic field that attracts the contacts to close; when the power is off, the contacts open due to the spring force.

[0089] In practical applications, the contact life of a relay is a crucial issue. Frequent switching operations lead to contact wear, reducing the relay's reliability. To extend the contact life, contact protection circuits can be employed. For example, an RC snubber circuit can be connected in parallel across the relay contacts. When the contacts open, the RC snubber circuit can absorb the arc energy between the contacts, reducing contact wear. Alternatively, relay models with longer contact life can be selected to improve the overall system reliability.

[0090] The input terminal of the PFC power unit is connected to the output terminal of the relay unit. It includes a switching assembly and PFC inductors L1-L3 corresponding to the three phases. The switching assembly includes power switch groups Q1-Q6 corresponding to the three phases, with each power switch group consisting of two power switches Q1 and Q2, Q3 and Q4, and Q5 and Q6. The power switches can be IGBTs (Insulated Gate Bipolar Transistors), which have the advantages of fast switching speed and high voltage withstand. The two power switches are connected in series between the positive bus capacitor C7 and the negative bus capacitor C8, and the series connection node is connected to the corresponding PFC inductors L1-L3. One end of the PFC inductors L1-L3 is connected to the output terminal of the relay unit, and the other end is connected to the corresponding power switch group. The PFC inductors L1-L3 are generally composed of a magnetic core and windings. The magnetic core can be a ferrite core, which has the characteristics of high permeability and low loss. By controlling the on and off of the power switches, the energy transfer from the PFC inductors to the bus energy storage unit can be adjusted, thereby regulating the bus voltage. For example, when the power switch is turned on, the PFC inductor stores energy; when the power switch is turned off, the PFC inductor releases the stored energy into the bus energy storage unit.

[0091] When designing a PFC inductor, its inductance value and saturation characteristics must be considered. The inductance value affects the turn-on and turn-off times of the power switch and the regulation effect on the bus voltage. If the inductance value is too small, it may increase the switching losses of the power switch; if the inductance value is too large, it will affect the regulation speed of the bus voltage. Simultaneously, PFC inductors may saturate under high current conditions, causing the inductance value to decrease and affecting the normal operation of the circuit. Ferrite cores with good saturation characteristics can be selected, or a multi-winding PFC inductor structure can be used to improve its anti-saturation capability.

[0092] The bus energy storage unit is connected to the output terminal of the PFC power unit and the other end of the soft-start resistor R1, including the positive bus capacitor C7 and the negative bus capacitor C8. These two capacitors are generally electrolytic capacitors, with a large capacitance, capable of storing a large amount of electrical energy to maintain stable positive and negative bus voltages. The advantage of electrolytic capacitors is their large capacitance, but they also have a certain equivalent series resistance (ESR). The impact of ESR on voltage stability needs to be considered when designing the circuit.

[0093] To reduce the impact of electrolytic capacitor ESR on bus voltage stability, multiple electrolytic capacitors can be connected in parallel. Parallel connection of multiple electrolytic capacitors reduces the overall ESR value and improves bus voltage stability. Alternatively, electrolytic capacitor models with lower ESR values ​​can be selected. Furthermore, the temperature characteristics of electrolytic capacitors also need attention. The capacitance and ESR values ​​of electrolytic capacitors change with temperature. In high-temperature environments, the performance of electrolytic capacitors may degrade. A temperature compensation circuit can be added to the circuit to automatically adjust circuit parameters according to temperature changes, ensuring bus voltage stability.

[0094] The voltage detection unit includes five detection branches: the first detection branch is connected to the input terminal of the first phase AC1 of the AC input unit, and is used to collect the peak voltage Vp1 of the first phase; the second detection branch is connected to the input terminal of the second phase AC2 of the AC input unit, and is used to collect the peak voltage Vp2 of the second phase; the third detection branch is connected to the input terminal of the third phase AC3 of the AC input unit, and is used to collect the peak voltage Vp3 of the third phase; the fourth detection branch is connected to the positive bus capacitor C7 of the bus energy storage unit, and is used to collect the positive bus voltage V7; the fifth detection branch is connected to the negative bus capacitor C8 of the bus energy storage unit, and is used to collect the negative bus voltage V8; the output terminal of each detection branch is connected to the signal input terminal of the MCU control unit.

[0095] To improve the accuracy and reliability of the voltage detection unit, redundant design can be implemented for the detection branches. For example, two identical voltage detection devices can be used in parallel for each detection branch. The MCU control unit compares and analyzes the output signals of the two detection devices. If the difference between the two signals is within a certain range, the detection result is considered valid; if the difference exceeds a certain range, an alarm signal can be issued to indicate a possible malfunction in the detection device. This improves the reliability of voltage detection and allows for the timely detection of potential problems.

[0096] The MCU control unit is connected to the voltage detection unit, relay unit, and PFC power unit. The MCU control unit receives voltage parameter signals transmitted from the voltage detection unit, processes the signals, and determines the voltage status. Based on the voltage status, the MCU control unit controls the on / off state of each relay in the relay unit and generates PWM drive signals to send to the PFC power unit. By adjusting the pulse width and frequency of the PWM drive signals, the MCU control unit controls the switching components to turn on and off, thereby dynamically adjusting the positive and negative bus voltages of the bus energy storage unit.

[0097] In terms of MCU control unit software design, a modular design approach can be adopted. Functions such as voltage detection signal processing, relay control, and PWM drive signal generation can be designed as independent modules, improving software maintainability and scalability. Simultaneously, to enhance system real-time performance, a real-time operating system (RTOS) can be employed. An RTOS can schedule and manage various tasks, ensuring the system can respond promptly to various events. For example, upon detecting an abnormal bus voltage, the RTOS can immediately schedule the corresponding task for processing, preventing further deterioration of the problem.

[0098] The implementation principle of this embodiment is as follows: This three-phase power factor correction circuit, through the coordinated operation of its various units, achieves power factor correction of the three-phase AC input and stable control of the bus voltage. The cooperation between the soft-start unit and the relay unit avoids inrush current during startup, the PFC power unit regulates the bus voltage, and the voltage detection unit and MCU control unit achieve real-time monitoring and precise control of the voltage. The entire circuit solves the problems existing in traditional three-phase PFC startup schemes, improves the reliability and stability of the circuit, and makes a significant improvement and contribution to existing technology. Through optimized design of each unit and software improvements, the performance and adaptability of the circuit are further enhanced, enabling it to better meet the needs of different practical application scenarios.

[0099] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method of starting a three-phase power factor correction circuit, characterized by, The starting method comprises: Step S1: Real-time detection of the first phase peak voltage, the second phase peak voltage, the third phase peak voltage, the positive bus voltage and the negative bus voltage of the three-phase alternating current input; Step S2: The positive bus capacitor and the negative bus capacitor are pre-charged through a soft start resistor, and after the pre-charging is completed, it is judged whether the positive bus voltage is greater than the first phase peak voltage minus a preset safety difference value and whether the negative bus voltage is greater than the first phase peak voltage minus the preset safety difference value, and if both conditions are met, the first relay is controlled to be attracted; Step S3: The MCU control unit adjusts the PWM drive signal to make the positive bus voltage and the negative bus voltage rise to a target value; Step S4: The positive bus voltage and the negative bus voltage are continuously adjusted until the positive bus voltage and the negative bus voltage are both greater than the second phase peak voltage and both greater than the third phase peak voltage, and the second relay and the third relay are controlled to be attracted; The preset safety difference in step S2 is V safe ≥I K1−max ×(R1+Req);I K1−max is the rated maximum allowable impact current of the first relay, R1 is the resistance value of the soft start resistor, and Req is the equivalent series resistance of each capacitor in the circuit at the initial stage of starting the circuit.

2. The start-up method of claim 1, wherein In step S3, the PWM drive signal is adjusted by adjusting the pulse width and frequency of the PWM drive signal to control the conduction time and switching frequency of the power switch tube, thereby controlling the rise of the positive bus voltage and the negative bus voltage.

3. The start-up method of claim 1, wherein In step S3, the target value is the maximum value of the second phase peak voltage and the third phase peak voltage.

4. The start-up method of claim 1, wherein In step S4, when the second relay and the third relay are controlled to be attracted, it is necessary to ensure that the positive bus voltage and the negative bus voltage have been stably in a state of being greater than the second phase peak voltage and being greater than the third phase peak voltage, so as to avoid large current and damage to the second relay and the third relay due to the large difference between the positive bus voltage and the second phase peak voltage and the third phase peak voltage and the large difference between the negative bus voltage and the second phase peak voltage and the third phase peak voltage.

5. A three-phase power factor correction circuit, characterized by, The starting method of the three-phase power factor correction circuit comprises: An alternating current input unit for connecting three-phase alternating current voltage and filtering the three-phase alternating current voltage to provide a filtered alternating current input power source for the three-phase power factor correction circuit; A soft start unit including a soft start resistor, one end of the soft start resistor being connected with a first phase output end of the alternating current input unit, the other end being connected with a bus energy storage unit, for pre-charging the bus energy storage unit at the initial stage of circuit starting to avoid impact current; A relay unit including a first relay, a second relay and a third relay, the input end of the relay unit being connected with the output end of the alternating current input unit, for controlling the on-off between the corresponding phase alternating current input and the power circuit; A PFC power unit, the input end of the PFC power unit being connected with the output end of the relay unit, including a switching assembly and a PFC inductor corresponding to three phases, for adjusting the size of the positive bus voltage and the negative bus voltage. A bus energy storage unit, including a positive bus capacitor and a negative bus capacitor, is connected with the output end of the PFC power unit, for storing electric energy to maintain stable positive bus voltage and negative bus voltage; A voltage detection unit is connected with the AC input unit and the bus energy storage unit, for collecting the first phase peak voltage, the second phase peak voltage, the third phase peak voltage, the positive bus voltage and the negative bus voltage of the three-phase AC input; An MCU control unit is connected with the voltage detection unit, the relay unit and the PFC power unit, for generating PWM drive signals according to voltage parameters and controlling the on-off of each relay.

6. The circuit of claim 5, wherein, The AC input unit includes a first phase AC voltage, a second phase AC voltage and a third phase AC voltage, corresponding to the first relay, the second relay and the third relay of the relay unit respectively, and the default state of each relay is off.

7. The circuit of claim 5, wherein, The switching assembly of the PFC power unit includes a power switch tube group corresponding to three phases, and the PFC power unit further includes a PFC inductor corresponding to three phases, one end of the PFC inductor being connected with the output end of the relay unit and the other end being connected with the power switch tube group of the corresponding phase.

8. The circuit of claim 7, wherein, Each power switch tube group includes two power switch tubes, which are connected in series between the positive bus capacitor and the negative bus capacitor, and the series node is connected with the PFC inductor of the corresponding phase; the gate of the power switch tube is connected with the PWM drive signal output end of the MCU control unit, and the conduction and turn-off of the power switch tube are controlled by the PWM drive signal to adjust the energy transmission of the PFC inductor to the bus energy storage unit.

9. The circuit of claim 5, wherein, The voltage detection unit includes five detection branches: The first detection branch is connected with the input end of the first phase of the AC input unit, for collecting the first phase peak voltage; The second detection branch is connected with the input end of the second phase of the AC input unit, for collecting the second phase peak voltage; The third detection branch is connected with the input end of the third phase of the AC input unit, for collecting the third phase peak voltage; The fourth detection branch is connected with the positive bus capacitor of the bus energy storage unit, for collecting the positive bus voltage; The fifth detection branch is connected with the negative bus capacitor of the bus energy storage unit, for collecting the negative bus voltage; and the output end of each detection branch is connected with the signal input end of the MCU control unit.

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