A method, apparatus and circuit for implementing power factor compensation

Abstract

The application provides a method, device and circuit for realizing power factor compensation. The method is applied to a controller connected with a plurality of switching tubes with a preset capacity. Each switching tube is connected with a bridge arm diode in a Vienna circuit in reverse parallel. The method comprises the following steps: detecting a current power factor of the Vienna circuit; when the current power factor is lower than a preset target power factor, controlling each switching tube to work in a phase interval in which reactive compensation current needs to be injected or absorbed to the power grid, so that the power factor of the Vienna circuit reaches the target power factor. The scheme forms a reactive compensation branch by connecting small capacity switching tubes in reverse parallel at both ends of each bridge arm diode on the basis of reserving the bridge arm diode of the Vienna circuit to undertake main power transmission, and the reactive compensation branch injects or absorbs reactive current by controlling the switching tubes to work in a specific phase interval of the power grid voltage, so that the overall power factor reaches a target value, and low-cost power factor compensation is realized.

Description

Technical Field

[0001] This invention relates to the field of circuit technology, and specifically to a method, apparatus, and circuit for achieving power factor compensation. Background Technology

[0002] Vienna rectifiers (such as three-phase Vienna rectifiers) serve as the front-end conversion unit for DC charging piles. They convert three-phase AC power into DC bus voltage through a three-level neutral clamp topology, and use active switches to achieve power factor correction (PFC) and reduce device voltage stress.

[0003] Existing charging piles in China use diodes as bridge arm rectifiers, which only support unidirectional power flow and do not have power factor compensation. While overseas charging piles use three-phase T-type three-level circuits that have power factor compensation, in order to ensure output power, the switching transistors are selected according to full power (which needs to handle both active and reactive power transmission), resulting in higher costs. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a method, apparatus and circuit for implementing power factor compensation, so as to achieve the purpose of low-cost power factor compensation.

[0005] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0006] The first aspect of this invention discloses a method for achieving power factor compensation, applied to a controller, wherein the controller is connected to a plurality of switching transistors with a preset capacity, each of the switching transistors being connected in reverse parallel with a bridge arm diode in the Vienna circuit, the method comprising:

[0007] Detect the current power factor of the Vienna circuit;

[0008] When the current power factor is lower than the preset target power factor, each of the switching transistors is controlled to operate within the phase interval where reactive power compensation current needs to be injected into or absorbed by the power grid, so that the power factor of the Vienna circuit reaches the target power factor.

[0009] Optionally, if the Vienna circuit is under three-phase unbalanced operating conditions, then detecting the current power factor of the Vienna circuit includes:

[0010] Detect the input current and input voltage of the Vienna circuit;

[0011] For the Vienna circuit, based on the input current and the corresponding input voltage, the ratio of active power to apparent power is calculated to obtain the current power factor;

[0012] When the current power factor is lower than the preset target power factor, each of the switching transistors is controlled to operate within the phase interval where reactive power compensation current needs to be injected into or absorbed from the power grid, so that the power factor of the Vienna circuit reaches the target power factor, including:

[0013] For the Vienna circuit, when the current power factor is less than the preset target power factor, each of the switching transistors is controlled to operate within the phase interval where reactive power compensation current needs to be injected into or absorbed by the power grid, so that the power factor of the Vienna circuit reaches the target power factor.

[0014] Optionally, the method further includes:

[0015] For the Vienna circuit, when the current power factor is greater than or equal to the target power factor, or when it is outside the phase interval where reactive power compensation current needs to be injected into or absorbed from the grid, the corresponding switches are controlled to remain off, so that the bridge arm diodes connected in reverse parallel with the switches transmit active power.

[0016] Optionally, the process of determining the preset capacity includes:

[0017] The preset capacity is determined based on the reactive power compensation required to raise the natural power factor of the Vienna circuit to the target power factor.

[0018] Optionally, determining the preset capacity based on the reactive power compensation power required to raise the natural power factor of the Vienna circuit to the target power factor includes:

[0019] Calculate the difference between the first tangent value corresponding to the natural power factor of the Vienna circuit and the second tangent value corresponding to the target power factor;

[0020] The reactive power compensation is obtained by multiplying the difference by the rated active power of the Vienna circuit.

[0021] The rated current value of each of the switching transistors is determined based on the reactive power compensation power, and the rated current value is used as the preset capacity.

[0022] A second aspect of this invention discloses a device for implementing power factor compensation, applied to a controller, wherein the controller is connected to a plurality of switching transistors with a preset capacity, each of the switching transistors being connected in reverse parallel with a bridge arm diode in the Vienna circuit, the device comprising:

[0023] A detection unit is used to detect the current power factor of the Vienna circuit;

[0024] The control unit is used to control each of the switching transistors to operate within the phase range where reactive power compensation current needs to be injected into or absorbed by the power grid when the current power factor is lower than the preset target power factor, so that the power factor of the Vienna circuit reaches the target power factor.

[0025] Optionally, if the Vienna circuit is under three-phase unbalanced operating conditions, the detection unit is specifically used for:

[0026] Detect the input current and input voltage of the Vienna circuit;

[0027] Detect the input current and input voltage of the Vienna circuit;

[0028] For the Vienna circuit, based on the input current and the corresponding input voltage, the ratio of active power to apparent power is calculated to obtain the current power factor;

[0029] The control unit is specifically used for:

[0030] For the Vienna circuit, when the current power factor is less than the preset target power factor, each of the switching transistors is controlled to operate within the phase interval where reactive power compensation current needs to be injected into or absorbed by the power grid, so that the power factor of the Vienna circuit reaches the target power factor.

[0031] Optionally, the control unit is further configured to:

[0032] For the Vienna circuit, when the current power factor is greater than or equal to the target power factor, or when it is outside the phase interval where reactive power compensation current needs to be injected into or absorbed from the grid, the corresponding switches are controlled to remain off, so that the bridge arm diodes connected in reverse parallel with the switches transmit active power.

[0033] Optionally, the device further includes:

[0034] The determining unit is used to determine the preset capacity based on the reactive power compensation power required to raise the natural power factor of the Vienna circuit to the target power factor.

[0035] A third aspect of the present invention discloses a circuit for implementing power factor compensation, the circuit comprising: a Vienna circuit, a controller, and a plurality of switching transistors;

[0036] The input terminal of the Vienna circuit is connected to the power grid; a switching transistor is connected in reverse parallel across the two ends of each bridge arm diode in the Vienna circuit.

[0037] The controller is connected to each of the switching transistors and is used to execute the method for achieving power factor compensation as described in any of the first aspects of the present invention.

[0038] Based on the above embodiments of the present invention, a method, apparatus, and circuit for achieving power factor compensation are provided. The method is applied to a controller, which connects multiple switching transistors with preset capacities. Each switching transistor is connected in reverse parallel with a bridge arm diode in a Vienna circuit. The method includes: detecting the current power factor of the Vienna circuit; when the current power factor is lower than a preset target power factor, controlling each switching transistor to operate within the phase interval where reactive power compensation current needs to be injected into or absorbed by the grid, so that the power factor of the Vienna circuit reaches the target power factor. This solution retains the main power transmission function of the bridge arm diodes in the Vienna circuit, and forms a reactive power compensation branch by connecting small-capacity switching transistors in reverse parallel across each bridge arm diode. By controlling them to operate within a specific phase interval of the grid voltage to inject or absorb reactive current, the overall power factor reaches the target value, achieving low-cost power factor compensation. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0040] Figure 1 This is a structural diagram of a three-phase Vienna circuit disclosed in an embodiment of the present invention;

[0041] Figure 2 This is a structural diagram of a three-phase T-type three-level circuit disclosed in an embodiment of the present invention;

[0042] Figure 3 This is a structural diagram of a circuit for implementing power factor compensation disclosed in an embodiment of the present invention;

[0043] Figure 4 This is a schematic diagram of the connection relationship between a three-phase Vienna circuit and a switching transistor disclosed in an embodiment of the present invention;

[0044] Figure 5 This is a flowchart of a method for implementing power factor compensation disclosed in an embodiment of the present invention;

[0045] Figure 6 This is a structural diagram of a device for implementing power factor compensation disclosed in an embodiment of the present invention. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0048] As can be seen from the background technology, the existing charging piles in China use diodes as bridge arm rectifier devices, which only support unidirectional power flow and do not have power factor compensation function. While the three-phase T-type three-level circuit used in overseas charging piles has power factor compensation function, in order to ensure output power, the switching transistors are selected according to full power (which needs to bear the transmission of active and reactive power), resulting in higher costs.

[0049] like Figure 1 The diagram shown is a structural diagram of a three-phase Vienna circuit disclosed in an embodiment of the present invention. The circuit includes: three-phase input inductors (L1, L2, L3), a three-phase rectifier bridge composed of six bridge arm diodes (D1-D6), DC bus capacitors (C1, C2), and built-in controllable switching transistors (Q1-Q6) connected between the midpoint of the three-phase rectifier bridge and the midpoint of the DC bus capacitor.

[0050] The input terminal of the three-phase input inductor is connected to the three-phase power grid, and the output terminal of the DC bus capacitor is connected to the downstream DC load. Six bridge arm diodes form a unidirectional three-phase bridge rectifier path to convert the three-phase AC power from the grid side into DC bus voltage; a built-in controllable switch is used to implement three-level midpoint clamping control to reduce device voltage stress.

[0051] However, the aforementioned three-phase Vienna circuit only supports unidirectional power flow, and the bridge arm diodes are uncontrollable devices, which means that the power factor of the circuit is naturally determined by the load characteristics and cannot be actively adjusted.

[0052] like Figure 2 The diagram shown is a structural diagram of a three-phase T-type three-level circuit disclosed in an embodiment of the present invention. This circuit adopts a fully controlled switching device topology to replace the uncontrolled diodes in the above-mentioned three-phase Vienna circuit.

[0053] Specifically, the three-phase T-type three-level circuit includes three-phase input inductors (L4, L5, L6) and a three-phase rectifier bridge composed of six switching transistors (Q7-Q12). These six transistors replace the six bridge arm diodes in a traditional rectifier bridge, and additional bidirectional switching devices are added to form a T-type three-level topology with bidirectional conduction capability. The input terminals of the three-phase input inductors are connected to the power grid, and the gates of the switching transistors are connected to a controller. The controller controls each switching transistor to achieve four-quadrant operation, active power transmission, and full-range reactive power compensation.

[0054] However, although the above-mentioned T-type three-level scheme has a complete power factor compensation function, in order to achieve bidirectional power flow and full power factor correction, Q7-Q12 all need to be configured with full power level according to the rated output power of the rectifier circuit, which leads to a significant increase in overall cost.

[0055] Therefore, this solution discloses a method, device, and circuit for achieving power factor compensation. In this solution, while retaining the Vienna circuit bridge arm diodes to carry out the main power transmission, small-capacity switching transistors are connected in reverse parallel across each bridge arm diode to form a reactive power compensation branch. By controlling the transistors to operate within a specific phase range of the grid voltage (i.e., conducting with a certain duty cycle within a specific phase range) to inject or absorb reactive current, the overall power factor reaches the target value, thus achieving low-cost power factor compensation.

[0056] like Figure 3 The diagram shown is a structural diagram of a circuit for implementing power factor compensation disclosed in an embodiment of the present invention. The circuit includes: a Vienna circuit (taking a three-phase Vienna circuit as an example), a controller, and multiple switching transistors with preset capacities. The switching transistors include: the nineteenth switching transistor Q19, the twentieth switching transistor Q20, the twenty-first switching transistor Q21, the twenty-second switching transistor Q22, the twenty-third switching transistor Q23, and the twenty-fourth switching transistor Q24.

[0057] like Figure 4 The diagram shown is a schematic representation of the connection relationship between a three-phase Vienna circuit and a switching transistor, as disclosed in an embodiment of the present invention.

[0058] In this three-phase Vienna circuit, the input terminal is connected to the power grid, and the output terminal is connected to the load; the three-phase Vienna circuit can be adopted... Figure 1 In the structure shown, each switch is connected in reverse parallel with a bridge arm diode in the three-phase Vienna circuit.

[0059] Specifically, the nineteenth switch Q19 is connected in reverse parallel across the seventh diode D7, with its drain connected to the cathode of the seventh diode D7 and its source connected to the anode of the seventh diode D7; the twentieth switch Q20 is connected in reverse parallel across the eighth diode D8, with its drain connected to the cathode of the eighth diode D8 and its source connected to the anode of the eighth diode D8; the twenty-first switch Q21 is connected in reverse parallel across the ninth diode D9, with its drain connected to the cathode of the ninth diode D9 and its source connected to the anode of the ninth diode D9; the twenty-second switch... Q22 is connected in reverse parallel across the tenth diode D10. The drain of the twenty-second switch Q22 is connected to the cathode of the tenth diode D10, and the source is connected to the anode of the tenth diode D10. The twenty-third switch Q23 is connected in reverse parallel across the eleventh diode D11. The drain of the twenty-third switch Q23 is connected to the cathode of the eleventh diode D11, and the source is connected to the anode of the eleventh diode D11. The twenty-fourth switch Q24 is connected in reverse parallel across the twelfth diode D12. The drain of the twenty-fourth switch Q24 is connected to the cathode of the twelfth diode D12, and the source is connected to the anode of the twelfth diode D12.

[0060] The rectifier circuit consisting of the three-phase Vienna circuit and multiple switching transistors is controlled by a controller (such as a DSP controller). The controller calculates the on / off control of each switching transistor based on the input and output parameters to meet the control requirements and thus achieve the power factor compensation function.

[0061] Specifically, the controller is connected to the gate of each switch and is used to implement a method for achieving power factor compensation by controlling the on and off of each switch to achieve power factor compensation.

[0062] It should be noted that, Figure 1 , Figure 2 , Figure 3 The switching transistors in the diagram are metal-oxide-semiconductor field-effect transistors (MOSFETs) or insulated-gate bipolar transistors (IGBTs). The internal body diodes are not shown for the sake of simplicity, but this does not affect the reverse parallel connection between the switching transistors and the bridge arm diodes or the implementation of this technical solution.

[0063] In this embodiment of the invention, power factor compensation currently only requires 0.9, and full-power compensation is not necessary. Therefore, the scheme of achieving power factor compensation by connecting diodes in parallel with MOSFETs based on the Vienna circuit has a cost advantage. The diodes are mainly responsible for outputting active power, while the MOSFETs only operate when reactive power compensation is required. Since power factor compensation only requires 0.9, the switching transistors only need to operate within a very small range, requiring only a small capacitance, which significantly reduces costs compared to existing technologies.

[0064] It should be noted that although the above embodiments of the present invention are illustrated using a three-phase Vienna circuit as an example, the core concept of this solution is to achieve differential reactive power compensation by connecting a small-capacity switching transistor in parallel across the diode. This is also applicable to single-phase Vienna circuits, and the principle is similar, so it will not be elaborated further.

[0065] It should be noted that the number of switching transistors corresponds one-to-one with the bridge arm diodes in the Vienna circuit. In other embodiments, the number of switching transistors may differ from the number of bridge arm diodes, for example, Figure 4 The circuit may only contain switching transistors Q19, Q21, and Q23, or only switching transistors Q20, Q22, and Q24. In this case, the Vienna circuit can operate for the corresponding half-cycle to perform reactive power compensation. If the three-phase balance issue does not need to be considered, only one or two phases may be equipped with switching transistors for reactive power compensation.

[0066] like Figure 5 The diagram shown is a flowchart of a method for implementing power factor compensation according to an embodiment of the present invention. This method is applied to a controller and includes the following steps:

[0067] Step S101: Detect the current power factor of the Vienna circuit.

[0068] In power systems, for three-phase Vienna circuits, the power factor is usually represented by an overall value, which is determined by the ratio of the total active power to the total apparent power. Under three-phase balanced operating conditions, since the voltage and current amplitudes of each phase are equal and the phases are symmetrical, the overall three-phase power factor is the same as the power factor of any individual phase. In this case, there is no need to distinguish between the single-phase power factor and the overall power factor.

[0069] However, under three-phase unbalanced conditions, there may be amplitude deviations or phase shifts in the voltage or current of each phase, resulting in different power factors for each phase. Furthermore, the overall three-phase power factor may differ from the power factor of each phase. In this case, the controller can also independently sample each phase and calculate the current power factor.

[0070] In the specific implementation of step S101, the input current and input voltage of the Vienna circuit are detected; for the Vienna circuit, based on the corresponding input current and corresponding input voltage, the ratio of active power to apparent power is calculated to obtain the current power factor.

[0071] It should be noted that, to achieve real-time monitoring of the power factor of the Vienna circuit, the controller synchronously acquires the input voltage and input current of the Vienna circuit through voltage sampling circuits and current sampling circuits respectively set in the input line. Specifically, the voltage sampling circuit is connected in parallel between the input terminal and the reference ground to detect the instantaneous value and phase information of the grid voltage in real time; the current sampling circuit is connected in series in the input line to detect the instantaneous value of the input current in real time.

[0072] In this embodiment of the invention, the detection method for the overall input voltage and overall input current (used to calculate the total active power and the total apparent power) is not limited.

[0073] After acquiring the above sampled data, the controller (such as a digital signal processor DSP) performs power factor calculation for the Vienna circuit: First, it calculates the instantaneous power based on the input voltage and input current, and obtains the active power by integrating or averaging the instantaneous power over one power frequency cycle; second, it calculates the apparent power based on the product of the input voltage and input current; finally, it calculates the ratio of active power to apparent power, which gives the current power factor.

[0074] The current power factor can be obtained through the above detection and calculation, providing a data basis for subsequent determination of whether reactive power compensation is needed. The current power factor can be the natural power factor of the Vienna circuit when the power factor compensation function is not enabled (i.e., the switching transistor is kept off), or it can be the real-time power factor during the compensation process.

[0075] Step S102: When the current power factor is lower than the preset target power factor, control each switch to operate in the phase range where reactive power compensation current needs to be injected into the grid or absorbed, so that the power factor of the Vienna circuit reaches the target power factor.

[0076] In step S102, the controller independently detects the current power factor in each cycle and independently determines whether the switch needs to operate within the phase interval (i.e., the target phase interval) where reactive power compensation current needs to be injected into or absorbed from the grid in the current cycle. When the current power factor in a certain cycle is greater than or equal to the target power factor, the switch remains off in that cycle; it only operates within the target phase interval of that cycle when the current power factor in a certain cycle is lower than the target power factor.

[0077] In another embodiment, after the controller determines that compensation is needed, it controls the switching transistor to work within the target phase interval for multiple consecutive cycles until the overall power factor is detected to be stable and meets the target.

[0078] The period refers to the power frequency period of the grid voltage, which is a complete time period of the power frequency sine wave. For example, a 50Hz power frequency system has a period of 20ms; a 60Hz power frequency system has a period of approximately 16.67ms.

[0079] It should be noted that there are two possible interpretations of the target phase interval mentioned above, both of which can achieve the reactive power compensation control in this case:

[0080] 1. The target phase range refers to the angular range defined based on the phase angle of the grid voltage waveform within a single cycle. For example, it is the ±30° angular range before and after the voltage zero-crossing point (0° or 180°). Under this understanding, the controller tracks the instantaneous phase angle of the grid voltage in real time through a phase-locked loop. When the grid voltage phase falls within the preset angular range, the switching transistor is triggered to operate.

[0081] 2. The target phase interval refers to a time window defined based on a single-cycle time axis. For example, the time range before and after the point where the grid voltage crosses zero. Under this understanding, the controller directly sets the start time and duration of the switching transistor's operation through an internal timer.

[0082] In conventional engineering practice, the power factor of a three-phase Vienna circuit is usually controlled as a whole. The controller obtains a unified current power factor by sampling and calculating the three-phase input voltage and current as a whole, and uses this to generate a duty cycle signal to control the on / off state of the switches in each phase. Depending on the actual compensation requirements, the control result may be that only one or a portion of the phase switches need to operate, or all three phase switches may operate simultaneously.

[0083] Optionally, under special operating conditions of severe three-phase imbalance, the power factors of each phase may differ significantly. In this case, the controller can also compensate for each phase separately, that is, only control the switching transistors of the specific phase whose current power factor is lower than the target power factor, while keeping the switching transistors of other phases off.

[0084] In the specific implementation of step S102, for the Vienna circuit, when the current power factor is less than the preset target power factor, each switch is controlled to work in the phase interval where reactive power compensation current needs to be injected into the grid or absorbed, so that the power factor of the Vienna circuit reaches the target power factor.

[0085] Specifically, the controller controls the switching transistor to conduct within a preset angle range before or after the grid voltage zero crossing or near the grid voltage peak, using high-frequency pulse width modulation to inject or absorb reactive power compensation current into the grid. By adjusting the duty cycle of the high-frequency pulse width modulation, the amplitude of the injected or absorbed reactive power compensation current is adjusted, thereby raising the power factor of the Vienna circuit to the target power factor.

[0086] In one embodiment, when the current power factor exhibits a lagging characteristic (i.e., the input current phase lags behind the grid voltage phase, and the circuit is inductive), the controller controls the switching transistor to conduct at high frequency around the time the grid voltage crosses zero, injecting capacitive reactive current (current leading voltage) into the grid to offset the inductive reactive power and improve the power factor.

[0087] When the current power factor exhibits a leading characteristic (i.e., the input current phase leads the grid voltage phase, and the circuit is capacitive), the controller controls the switching transistor to turn on near the peak of the grid voltage to absorb the inductive reactive current of the grid (current lags behind voltage) in order to reduce the capacitive reactive component and make the power factor approach the target value.

[0088] In one embodiment, for the Vienna circuit, when the current power factor is greater than or equal to the target power factor, or when it is outside the phase interval where reactive power compensation current needs to be injected into or absorbed from the grid, the corresponding individual switches are controlled to remain off, so that the bridge arm diodes connected in reverse parallel with the switches transmit active power.

[0089] Understandably, for a phase whose current power factor has reached or exceeded the target power factor, the controller controls the corresponding switching transistors to remain in the off state, and the main power transmission is undertaken by the bridge arm diodes connected in reverse parallel with the switching transistors, ensuring efficient system operation.

[0090] In this embodiment of the invention, to achieve low-cost power factor compensation, it is necessary to pre-determine the capacity of each switch connected in parallel in the Vienna circuit. The specific determination method is as follows:

[0091] The preset capacity is determined based on the reactive power compensation required to raise the natural power factor of the Vienna circuit to the target power factor.

[0092] More specifically, the difference between the first tangent value corresponding to the natural power factor of the Vienna circuit and the second tangent value corresponding to the target power factor is calculated; the reactive power compensation is obtained by multiplying the difference by the rated active power of the Vienna circuit; the current rating of each switch is determined according to the reactive power compensation, and the current rating is used as the preset capacity.

[0093] To facilitate understanding of the above calculation process, the calculation principle is explained in detail below:

[0094] The reactive power (in kVAR) required to raise the power factor from its current value to 0.9 depends on the active power (kW) and the power factor before compensation.

[0095] The formula for calculating reactive power compensation is: Qc = P × (tanφ1 - tanφ2).

[0096] Where P is the active power (kW), φ1 is the power factor angle before compensation, and φ2 is the power factor angle after compensation (cosφ2=0.9).

[0097] Optionally, the reactive power compensation power selected in engineering should be higher than the calculated value to allow for a certain margin.

[0098] First, calculate the tangent of φ1 (i.e., the first tangent corresponding to the natural power factor) based on the power factor before compensation, cosφ1 (i.e., the natural power factor): tanφ1=√(1 / cos²φ1-1); Second, calculate the tangent of the power factor after compensation, cosφ2=0.9 (i.e., the target power factor), tanφ2≈0.4843; Finally, substitute into the formula Qc=P×(tanφ1-0.4843) to obtain the reactive power compensation power.

[0099] For example:

[0100] If the active power P = 100kW and the power factor before compensation cosφ1 = 0.8, then tanφ1 = √(1 / 0.8²-1) ≈ 0.75, and the reactive power compensation power Qc ≈ 100 × (0.75 - 0.4843) ≈ 26.57 kVAR.

[0101] If P = 300kW and cosφ1 = 0.75, then tanφ1 ≈ 0.8819 and Qc ≈ 300 × (0.8819 - 0.4843) ≈ 119 kVAR.

[0102] If the compensated power factor cosφ2=0.95 (i.e. the target power factor), its corresponding tangent value tanφ2≈0.3268. Similarly, taking the active power P=100kW and the power factor before compensation cosφ1=0.8 as an example, the reactive power compensation power Qc≈100×(0.75-0.3268)≈32.32kVAR.

[0103] In practical applications, it should be noted that: reactive power compensation power needs to be calculated based on the specific active power and the original power factor. The formula is applicable to three-phase AC systems. If the original power factor is already higher than 0.9, no compensation is required.

[0104] The power factor of the power grid before compensation (i.e., the natural power factor) varies depending on the type of power grid, load composition, and operating conditions.

[0105] For example:

[0106] Distribution network (6kV~10kV): Natural power factor is generally 0.8~0.85;

[0107] Substations (35-110kV): Natural power factor is typically between 0.85 and 0.9;

[0108] Rural power distribution networks (agricultural power grids): have a low natural power factor, mostly between 0.5 and 0.6;

[0109] Industrial user side (uncompensated): The natural power factor of the comprehensive load ranges from 0.6 to 0.9, with enterprises with large-capacity synchronous motors or pure electrolytic loads reaching a higher value (close to 0.9).

[0110] Since inductive loads (such as motors and transformers) dominate the power grid, the natural power factor is generally less than 1, and in most cases it is in the range of 0.7 to 0.9.

[0111] To meet the operational requirements of the power system, the power factor is usually raised to above 0.9 through reactive power compensation, and in some cases, it is required to reach 0.95.

[0112] In summary, the natural power factor of the power grid before compensation is usually between 0.5 and 0.9, with the specific value depending on the grid level and load characteristics.

[0113] In some charging pile scenarios, the natural power factor input from the grid is generally not less than 0.8. In this case, setting the capacity of the switching transistor (or the maximum power carrying capacity, maximum current carrying capacity) to 1 / 3 of that of the bridge arm diode is sufficient to compensate the power factor to 0.9, or even 0.95.

[0114] Based on the above-described method for achieving power factor compensation disclosed in the embodiments of the present invention, in this scheme, while retaining the Vienna circuit bridge arm diodes to carry out the main power transmission, small-capacity switching transistors are connected in reverse parallel across each bridge arm diode to form a reactive power compensation branch. By controlling them to operate within a specific phase range of the grid voltage to inject or absorb reactive current, the overall power factor reaches the target value, thus achieving low-cost power factor compensation.

[0115] Corresponding to the method for achieving power factor compensation disclosed in the above embodiments of the present invention, such as Figure 6 The diagram shown is a structural diagram of a device for implementing power factor compensation according to an embodiment of the present invention. This device is applied to a controller and includes:

[0116] The detection unit 601 is used to detect the current power factor of the Vienna circuit;

[0117] The control unit 602 is used to control each switch to operate in the phase range where reactive power compensation current needs to be injected into the grid or absorbed when the current power factor is lower than the preset target power factor, so that the power factor of the Vienna circuit reaches the target power factor.

[0118] Optionally, the detection unit 601 is specifically used for:

[0119] Detect the input current and input voltage of the Vienna circuit;

[0120] For the Vienna circuit, the ratio of active power to apparent power is calculated based on the input current and the corresponding input voltage to obtain the current power factor;

[0121] Accordingly, the control unit 602 is specifically used for:

[0122] For the Vienna circuit, when the current power factor is less than the preset target power factor, each switch is controlled to operate in the phase range where reactive power compensation current needs to be injected into the grid or absorbed, so that the power factor of the Vienna circuit reaches the target power factor.

[0123] Optionally, the control unit 602 is also used for:

[0124] For the Vienna circuit, when the current power factor is greater than or equal to the target power factor, or when it is outside the phase interval where reactive power compensation current needs to be injected into or absorbed from the grid, the corresponding switches are controlled to remain off, so that the bridge arm diodes connected in reverse parallel with the switches can transmit active power.

[0125] Optionally, the device also includes:

[0126] The determination unit is used to determine the preset capacity based on the reactive power compensation power required to raise the natural power factor of the Vienna circuit to the target power factor.

[0127] Optional, define the unit, specifically for:

[0128] Calculate the difference between the first tangent value corresponding to the natural power factor and the second tangent value corresponding to the target power factor of the Vienna circuit;

[0129] The reactive power compensation is obtained by multiplying the difference by the rated active power of the Vienna circuit.

[0130] The rated current of each switch is determined based on the reactive power compensation power, and the rated current is used as the preset capacity.

[0131] Based on the above-described embodiment of the present invention, a device for realizing power factor compensation is disclosed. In this solution, while retaining the Vienna circuit bridge arm diodes to carry out the main power transmission, small-capacity switching transistors are connected in reverse parallel across each bridge arm diode to form a reactive power compensation branch. By controlling the diodes to operate within a specific phase range of the grid voltage to inject or absorb reactive current, the overall power factor reaches the target value, thus achieving low-cost power factor compensation.

[0132] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the descriptions in the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0133] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0134] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for achieving power factor compensation, characterized in that, Applied to a controller, wherein the controller connects multiple switching transistors with preset capacities, each of the switching transistors being connected in reverse parallel with a bridge arm diode in the Vienna circuit, the method includes: Detect the current power factor of the Vienna circuit; When the current power factor is lower than the preset target power factor, each of the switching transistors is controlled to operate within the phase interval where reactive power compensation current needs to be injected into or absorbed by the power grid, so that the power factor of the Vienna circuit reaches the target power factor.

2. The method according to claim 1, characterized in that, The detection of the current power factor of the Vienna circuit includes: Detect the input current and input voltage of the Vienna circuit; For the Vienna circuit, based on the input current and the corresponding input voltage, the ratio of active power to apparent power is calculated to obtain the current power factor; When the current power factor is lower than the preset target power factor, each of the switching transistors is controlled to operate within the phase interval where reactive power compensation current needs to be injected into or absorbed from the power grid, so that the power factor of the Vienna circuit reaches the target power factor, including: For the Vienna circuit, when the current power factor is less than the preset target power factor, each of the switching transistors is controlled to operate within the phase interval where reactive power compensation current needs to be injected into or absorbed by the power grid, so that the power factor of the Vienna circuit reaches the target power factor.

3. The method according to claim 2, characterized in that, The method further includes: For the Vienna circuit, when the current power factor is greater than or equal to the target power factor, or when it is outside the phase interval where reactive power compensation current needs to be injected into or absorbed from the grid, the corresponding switches are controlled to remain off, so that the bridge arm diodes connected in reverse parallel with the switches transmit active power.

4. The method according to claim 1, characterized in that, The process of determining the preset capacity includes: The preset capacity is determined based on the reactive power compensation required to raise the natural power factor of the Vienna circuit to the target power factor.

5. The method according to claim 4, characterized in that, The determination of the preset capacity based on the reactive power compensation power required to raise the natural power factor of the Vienna circuit to the target power factor includes: Calculate the difference between the first tangent value corresponding to the natural power factor of the Vienna circuit and the second tangent value corresponding to the target power factor; The reactive power compensation is obtained by multiplying the difference by the rated active power of the Vienna circuit. The rated current value of each of the switching transistors is determined based on the reactive power compensation power, and the rated current value is used as the preset capacity.

6. A device for realizing power factor compensation, characterized in that, Applied to a controller, the controller is connected to multiple switching transistors with preset capacities, each of the switching transistors being connected in reverse parallel with a bridge arm diode in the Vienna circuit, the device comprising: A detection unit is used to detect the current power factor of the Vienna circuit; The control unit is used to control each of the switching transistors to operate within the phase range where reactive power compensation current needs to be injected into or absorbed by the power grid when the current power factor is lower than the preset target power factor, so that the power factor of the Vienna circuit reaches the target power factor.

7. The apparatus according to claim 6, characterized in that, The detection unit is specifically used for: Detect the input current and input voltage of the Vienna circuit; For the Vienna circuit, based on the input current and the corresponding input voltage, the ratio of active power to apparent power is calculated to obtain the current power factor; The control unit is specifically used for: For the Vienna circuit, when the current power factor is less than the preset target power factor, each of the switching transistors is controlled to operate within the phase interval where reactive power compensation current needs to be injected into or absorbed by the power grid, so that the power factor of the Vienna circuit reaches the target power factor.

8. The apparatus according to claim 7, characterized in that, The control unit is also used for: For the Vienna circuit, when the current power factor is greater than or equal to the target power factor, or when it is outside the phase interval where reactive power compensation current needs to be injected into or absorbed from the grid, the corresponding switches are controlled to remain off, so that the bridge arm diodes connected in reverse parallel with the switches transmit active power.

9. The apparatus according to claim 6, characterized in that, The device further includes: The determining unit is used to determine the preset capacity based on the reactive power compensation power required to raise the natural power factor of the Vienna circuit to the target power factor.

10. A circuit for implementing power factor compensation, characterized in that, The circuit includes: a Vienna circuit, a controller, and multiple switching transistors; The input terminal of the Vienna circuit is connected to the power grid; a switching transistor is connected in reverse parallel across the two ends of each bridge arm diode in the Vienna circuit. The controller is connected to each of the switching transistors and is used to perform the method for achieving power factor compensation as described in any one of claims 1 to 5.

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