Charging power supply circuit and control method thereof

Abstract

The present invention discloses a charging power supply circuit and its control method. The charging power supply circuit includes a PFC circuit, a driver module, and a high-voltage output circuit and a low-voltage output circuit connected to the PFC circuit. The PFC circuit is connected to the AC mains. The driver module is used to set the PFC circuit's operating range to a range near the zero point of the AC input voltage. The technical solution of the present invention can achieve the requirements of the isolation topology while reducing the size and cost of the PFC circuit.

Description

Technical Field

[0001] This patent relates to the field of power supply technology, and in particular to a charging power supply circuit and a control method thereof. Background Art

[0002] Currently, in the design of AC-to-DC charging power supplies, such as on-board chargers, a PFC circuit is required in the front-end to maintain power factor. At the same time, to ensure electrical safety isolation, an isolated DC-DC circuit topology is added in series with the PFC circuit. This is commonly referred to as a two-stage series design. In this two-stage series design, both the PFC and DC-DC circuits are designed for maximum output power. The PFC circuit requires high-performance PFC switches and a larger PFC inductor, resulting in a bulky and costly charging power supply circuit. Summary of the Invention

[0003] To address the issues of large size and high cost of charging power supply circuits in the prior art, the present invention provides a charging power supply circuit and a control method thereof. By employing this method, a lower-performance PFC switch tube and a smaller PFC inductor can be used, thereby reducing the size and cost of the PFC circuit.

[0004] In an embodiment of the present invention, a charging power supply circuit is provided, characterized by including a PFC circuit, a drive module, and a high-voltage output circuit and a low-voltage output circuit connected to the PFC circuit. The PFC circuit is connected to the AC mains, and the drive module is configured to set the operating interval of the PFC circuit to a time interval near the zero point of the AC input voltage.

[0005] In the embodiment of the present invention, the operating phase interval of the PFC circuit is

[0006] Where n is a natural number, f is the frequency of the input AC power supply, and Tpfc is the operating time of the PFC switch in half a current cycle. Tpfc is calculated using the following formula:

[0007]

[0008] Wherein, Vin is the voltage of the input power supply, Iin is the current of the input power supply, Po2 is the output power of the low-voltage output circuit, and Po is the total output power of the charging power supply circuit.

[0009] In an embodiment of the present invention, the PFC circuit includes a PFC switch tube Qpfc, a rectifier bridge Drect, a PFC inductor L1, a freewheeling diode D1, a bypass diode D2, and a PFC output bus capacitor Cbus. The freewheeling diode D1 is connected in series to the positive output bus of the rectifier bridge Drect, the PFC inductor L1 and the freewheeling diode D1 are connected in series between the positive and negative electrodes of the freewheeling diode D1, the PFC switch tube Qpfc is connected in series between the connection point of the PFC inductor L1 and the freewheeling diode D1 and the negative output bus of the rectifier bridge Drect, and the control electrode of the switch tube Qpfc is connected to the drive module.

[0010] In an embodiment of the present invention, the control module is further configured to set the output current of the high-voltage output circuit according to the real-time value of the AC voltage during a time interval when the PFC circuit is not operating, so as to achieve tracking of the input voltage and input current.

[0011] In an embodiment of the present invention, the control module sets the output current Io1(t) of the high-voltage output circuit according to the following formula:

[0012]

[0013] Wherein, Po is the total output power of the charging power supply circuit, Vo1 is the output voltage of the high-voltage output circuit, and Po2 is the output power of the low-voltage output circuit.

[0014] In an embodiment of the present invention, a control method for the above-mentioned charging power supply circuit is further provided, which includes:

[0015] Sample the AC input voltage and calculate the frequency of the AC voltage and the effective value of the input voltage;

[0016] Calculating the operating time Tpfc of the PFC switch tube within half a current cycle using the set power of the low-voltage output circuit, the input instantaneous voltage, and the input instantaneous current;

[0017] The working phase interval of the PFC circuit is calculated using the AC voltage frequency f n is a natural number.

[0018] In an embodiment of the present invention, the control method of the charging power supply circuit further includes: achieving tracking of input voltage and input current in the operating range of the PFC circuit.

[0019] In the embodiment of the present invention, the operating time Tpfc of the PFC switch tube is calculated by the following formula:

[0020]

[0021] Wherein, f is the frequency of the input AC power supply, Vin is the voltage of the input power supply, Iin is the current of the input power supply, Po2 is the output power of the low-voltage output circuit, and Po is the total output power of the charging power supply circuit.

[0022] In an embodiment of the present invention, the control method of the charging power supply circuit further includes:

[0023] During the non-operating time interval of the PFC circuit, the zero-crossing phase of the AC voltage is locked, and the high-voltage output current is set according to the real-time value of the AC voltage, thereby achieving tracking of the input voltage and input current.

[0024] In the embodiment of the present invention, the output current Io1(t) of the high-voltage output circuit is set according to the following formula:

[0025]

[0026] Wherein, Po is the total output power of the charging power supply circuit, Vo1 is the output voltage of the high-voltage output circuit, and Po2 is the output power of the low-voltage output circuit.

[0027] Compared with the prior art, the charging power supply circuit and control method thereof of the present invention set the operating range of the PFC circuit to a time interval near the zero point of the AC input voltage. This can reduce the switching frequency of the PFC switch tube and the parameter requirements of the PFC inductor, thereby reducing the parameters of the PFC switch tube and PFC inductor in the PFC circuit, reducing the size and cost of the PFC circuit. In addition, input current and voltage tracking are performed separately according to the different operating states of the PFC circuit near the zero point of the input voltage to achieve power factor correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is described in detail below with reference to the embodiments and accompanying drawings, in which:

[0029] Figure 1 FIG. 4 is a topological diagram of a charging power supply circuit according to an embodiment of the present invention.

[0030] Figure 2 It is the input AC voltage waveform.

[0031] Figure 3 It is the voltage waveform after rectification.

[0032] Figure 4 This is a schematic diagram of the time-sharing working range of the PFC circuit.

[0033] Figure 5 This is a schematic diagram of the DC_BUS voltage waveform output by the PFC circuit.

[0034] FIG6(A) and FIG6(B) are schematic diagrams of output current waveforms of the high-voltage output circuit at different output powers of the low-voltage output circuit, respectively.

[0035] Figure 7 It is a flow chart of the entire control process.

[0036] Figure 8 This is a topology diagram of a PFC circuit according to another embodiment of the present invention.

[0037] Figure 9 This is a topology diagram of a DCDC circuit according to another embodiment of the present invention.

[0038] Figure 10 This is a simulation diagram of the time-sharing operation of the PFC circuit.

[0039] Figure 11 This is one of the simulated output current waveforms of the control method of the present invention.

[0040] Figure 12 This is the second simulated output current waveform diagram of the control method of the present invention.

[0041] Figure 13 This is a simulated input current waveform diagram of the control method of the present invention. DETAILED DESCRIPTION

[0042] The following describes embodiments of the present invention in detail, with examples of the embodiments illustrated in the accompanying drawings. Identical or similar reference numerals denote identical or similar components or elements having identical or similar characteristics. Conventional circuit operations, such as changing current / voltage adaptation through connection resistance, are readily understood by those skilled in the art and are not described in detail in the specific embodiments. The embodiments described below with reference to the accompanying drawings are illustrative and intended only to explain the present invention and are not to be construed as limiting the present invention.

[0043] Figure 1 The topology of the charging power supply circuit implemented by the control method of the present invention is shown as follows: Figure 1 As shown, the circuit topology is a three-port architecture, which includes a PFC circuit, a DCDC circuit and a driving module, wherein the DCDC circuit includes a high-voltage output circuit and a low-voltage output circuit. Figure 1In the figure, VAC is the AC mains input port, and Vo1 and Vo2 are DC output ports. Specifically, the PFC circuit includes: input AC voltage VAC, slow start resistor R, relay K, rectifier bridge DRECT, PFC inductor L1, high-frequency switch tube QPFC, freewheeling diode D1, bypass diode D2, and PFC output bus capacitor Cbus. The high-voltage output circuit outputs voltage Vo1, which is used to charge the high-voltage battery, and includes: switch tubes Q1 to Q8, inductor Lr, capacitor Cr, transformer T1, capacitor C2, and capacitor C4. The low-voltage output circuit outputs voltage Vo2, which is used to charge the low-voltage battery and requires constant power, and includes: switch tubes Q9 to Q11, capacitor C3, inductor L2, and diode D3. The driving module is used to generate driving signals for each switch tube in the charging power supply circuit.

[0044] Figure 2 shows the input AC voltage waveform, as Figure 2 As shown, the AC voltage VAC is a sine wave, where the relationship between the real-time voltage and time is as follows:

[0045]

[0046] In formula (1), Vin is the effective value of the AC voltage, and f is the AC voltage frequency. After being rectified by the diode DRECT, the voltage VRECT becomes Figure 3 The steamed bun-shaped waveform at the zero-crossing point is shown. At this time, the relationship between real-time voltage and time is as follows:

[0047]

[0048] In formula (2), Vin is the effective value of the AC voltage, and f is the frequency of the AC voltage.

[0049] The operating time of the PFC circuit is determined by the DC power Po2 of the low-voltage output circuit. The input power is obtained by inverse calculation of the efficiency of the low-voltage output DC power Po2. According to the law of conservation of energy, it is as follows:

[0050]

[0051]

[0052] In equations (3.1) and (3.2), Iin(t) is the input instantaneous current, Vin(t) is the input instantaneous voltage, and Tpfc is the time. The input instantaneous current can be given by the following formula:

[0053]

[0054] In formula (4), f is the AC voltage frequency, Iin is the effective value of the input current, and the effective value of the input current is determined by the total output power Po of the charging power supply circuit:

[0055] Vin·Iin·η=Po (5)

[0056] In formula (5), Vin is the effective value of the input voltage, Iin is the effective value of the input current, and η is the power conversion efficiency value.

[0057] From the above formula (1) to formula (5), we can get the following formula:

[0058]

[0059] From formula (6), we can see that when determining P o2 After determining Po and input voltage VAC, the time Tpfc can be calculated under the condition that the input voltage VAC is known. The phase Phase of PFC operation can be obtained by Tpfc and the known mains cycle. The time Tpfc and phase Phase satisfy the following relationship:

[0060]

[0061] So, if Figure 4 As shown, is the operating range of the PFC circuit, where n is a natural number. After the PFC circuit operates in the above range, the waveform of the output voltage DC_BUS of the PFC circuit is as follows Figure 5 As shown, at this time, the PFC output voltage DC_BUS is a steamed bun wave voltage that does not cross zero.

[0062] In the control method of the present invention, the switch tube Q PFC The PFC switches operate only for a period of time near the voltage zero crossing. The main purposes are: (1) to ensure that the AC voltage and current follow each other near the zero crossing point; (2) to reduce the transformer turns ratio limit in the downstream DCDC circuit, facilitating transformer design; and (3) to ensure that the low voltage Vo2 can output constant power near the AC voltage zero crossing. At other times, the PFC switch does not operate, and power is transferred to the downstream load through the bypass diode D2. The input current tracking is partially adjusted by the downstream DCDC circuit.

[0063] When the PFC circuit is not working, the input current and input voltage follow the control and are realized by the output voltage Vo1 of the subsequent DCDC circuit. The input terminal of the DCDC circuit is connected to the output DC_BUS of the PFC circuit, and the voltage is as follows: Figure 5The steamed bun wave shown does not pass through zero; the load connected to the output terminal of the DCDC circuit's output voltage Vo1 is a high-voltage battery, which is a stable DC voltage, that is, the output voltage Vout is a stable DC voltage. The high-voltage output current Io1 is controlled by the controller with a current reference to achieve power control of the first output. Since the input voltage and input current are both sinusoidal waves, that is, the input instantaneous power is: Pin(t) = VAC(t) * Iin(t); the output power is Po = Vout * Io1; and Vout is a DC voltage. The PFC circuit operates in part of the time interval. To ensure that the input voltage and input current follow each other, it is necessary to ensure that the PFC circuit is in the non-operating time interval. At this time, the input instantaneous power and the output instantaneous power are equal. Combining the law of conservation of energy and Equations 1, 4, and 5, we can obtain:

[0064]

[0065] In Equation 7, Vin is the RMS input voltage, Iin is the RMS input current, η is the efficiency, and Io1 is the high-voltage output current. The output voltage Vo1 is actually connected to a high-voltage battery, which is a stable DC voltage. Since the output voltage Vout is a DC voltage, Equation 7 can be used to convert the instantaneous output current Io1(t) into:

[0066]

[0067] Since the output voltage Vout is a DC voltage, during the charging process, changing the output current value according to formula (9) can ensure that the input voltage and current follow each other. At this time, the output current waveform is shown in Figure 6(A) and Figure 6(B) below, where Figure 6(A) is a schematic diagram of the current waveform of the output current Io1 of the high-voltage output circuit when Po2=0W; Figure 6(B) is a schematic diagram of the current waveform of the output current Io1 of the high-voltage output circuit when Po2=2000W.

[0068] According to the above analysis, if Figure 7 As shown, the control method steps of the present invention are as follows:

[0069] S701. Sample the input AC voltage and the voltage after diode rectification respectively, and calculate the frequency of the AC voltage and the effective value of the input voltage;

[0070] S702. Sample input AC current;

[0071] S703. Calculate the PFC circuit time and PFC operating phase using the set low-voltage circuit output power, input instantaneous voltage, and input instantaneous current;

[0072] S704. Calculate the PFC operating time interval using time and AC voltage frequency;

[0073] S705. Follow the input voltage and input current in the AC voltage zero-crossing region;

[0074] S706. During the non-working time interval of the PFC, the zero-crossing phase of the AC voltage is locked and the high-voltage output current is set according to the real-time value of the AC voltage;

[0075] S707: Implement input voltage and input current tracking during the non-operating time interval of the PFC.

[0076] The charging power supply circuit of the present invention can also be implemented in other ways. For example, in another embodiment, the PFC circuit topology can also be as follows: Figure 8 In another embodiment, the DCDC circuit topology may also be as follows: Figure 9 The architecture shown.

[0077] In a specific embodiment, the total output power Po of the charging power supply circuit is 6600 W; the high-voltage battery voltage Vo1 is 350 V; the effective value of the input voltage Vin is 220 V; the AC voltage frequency f is 50 Hz; the conversion efficiency η is 94%; and the required power Vo2 is set to Po2 = 2000 W. Then:

[0078] According to formula 5, Iin = 31.92A; according to formula 3.1, Tpfc = 2.1815ms; according to formula 6, the PFC operating phase angle phase = 0.218π = 39.24°, so the PFC operating time interval is:

[0079] {[n*π, n*π+0.218π]; [(n+1)*π-0.218π, (n+1)π]}, n≥0 and is an integer;

[0080] Then calculate the output average current Io1ave = 18.86A; set the current of the high-voltage output Io1 according to formula 8:

[0081] Io1ref=37.72A*sin(2*π*f*t)*sin(2*π*f*t)-Po2 / Vo1

[0082] like Figure 10 The figure shows the simulation timing diagram of VAC, VRECT, and PFC driver, where the PFC driver only operates for a period of time near the AC voltage zero crossing.

[0083] Figure 11 When Po2=0, the waveform of the output current Io1ref and the high-voltage output current Io1 is shown in the figure. From the figure, it can be seen that the envelope of the output current waveform is consistent with the setting. The average current within the cycle is also within the error range of the accuracy requirement. Table 1 shows the simulation data of the high-voltage output current Po1 when Po2 = 0W.

[0084] Table 1: Po2 = 0W, Po1 output simulation data

[0085] Theoretically calculated current given average value Io1ave Simulated output current average value Accuracy 18.86A 19.027A 0.88％

[0086] Figure 12 The waveforms of the output current Io1ref and the high-voltage output current Io1 are shown when Po2 = 2000W. From the figure, it can be seen that the high-voltage output current Io1 is 0 in areas A and B in the figure. The high-voltage output current Io1 is consistent with the demand. Table 1 shows the simulation data of the high-voltage output current Po1 when Po2 = 2000W.

[0087] Table 1: Po2 = 2000W, Po1 output simulation data

[0088] Theoretically calculated current given average value Io1ave Simulated output current average value Accuracy 13.14A 13.028A -0.85％

[0089] Figure 13 The waveforms of the corresponding input voltage VAC, input current Iin and output voltage DC_BUS of the PFC circuit are shown in the figure. Figure 7 The flow chart operation enables the input current to track the input voltage. Table 3 shows the calculated device currents for partial switching control and continuous operation of the traditional PFC switch tube. This comparison shows that partial switching control significantly reduces the currents of the switch tube, the freewheeling tube, and the PFC circuit, thereby reducing device size and cost.

[0090] Table 3: Comparison of operating current using partial control and continuous switching

[0091]

[0092] In the description of the present invention, it should be noted that, unless otherwise specified or limited, the terms "connected," "including," "another," etc. should be understood in a broad sense. Those skilled in the art will understand the specific meanings of the terms based on specific circumstances. As used herein, the singular forms "a" and "an" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0093] In this specification, the schematic representations of the terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples.

[0094] Although embodiments of the present invention have been shown, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A charging power supply circuit, characterized in that: The system comprises a PFC circuit, a driving module, and a high-voltage output circuit and a low-voltage output circuit connected to the PFC circuit. The PFC circuit is connected to the AC mains. The driving module is configured to set the operating range of the PFC circuit to a range near the zero point of the AC input voltage. The working phase interval of the PFC circuit is Where n is a natural number, f is the frequency of the input AC power supply, and Tpfc is the operating time of the PFC switch in the PFC circuit within half a current cycle. Tpfc is calculated using the following formula: Among them, Po2 is the output power of the low-voltage output circuit, and Po is the total output power of the charging power supply circuit.

2. The charging power supply circuit according to claim 1, wherein: The PFC circuit includes a PFC switch tube Qpfc, a rectifier bridge Drect, a PFC inductor L1, a freewheeling diode D1, a bypass diode D2, and a PFC output bus capacitor Cbus. The freewheeling diode D1 is connected in series to the positive output bus of the rectifier bridge Drect, the PFC inductor L1 and the freewheeling diode D1 are connected in series between the positive and negative electrodes of the freewheeling diode D1, the PFC switch tube Qpfc is connected in series between the connection point of the PFC inductor L1 and the freewheeling diode D1 and the negative output bus of the rectifier bridge Drect, and the control electrode of the switch tube Qpfc is connected to the drive module.

3. The charging power supply circuit according to claim 1, wherein: The driving module is further configured to set the output current of the high-voltage output circuit according to the real-time value of the AC voltage during a time interval when the PFC circuit is not operating, so as to achieve tracking of the input voltage and input current.

4. The charging power supply circuit according to claim 1, wherein: The driving module sets the output current Io1(t) of the high-voltage output circuit according to the following formula: Wherein, Vin is the voltage of the input power supply, Iin is the current of the input power supply, Po is the total output power of the charging power supply circuit, Vo1 is the output voltage of the high-voltage output circuit, and Po2 is the output power of the low-voltage output circuit.

5. A control method using the charging power supply circuit according to any one of claims 1 to 4, characterized in that: include: The input voltage and the input current follow each other in the working range of the PFC circuit.

6. The control method of the charging power supply circuit according to claim 5, characterized in that: Also includes: During the non-operating time interval of the PFC circuit, the zero-crossing phase of the AC voltage is locked, and the high-voltage output current is set according to the real-time value of the AC voltage, thereby achieving tracking of the input voltage and input current.

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