Current handling methods, on-board chargers and related devices

Abstract

This invention discloses a current processing method, an on-board charger, and related devices. The bus voltage control unit in the on-board charger includes a first control unit, a notch filter unit, and a power feedforward unit. The notch filter unit filters out the double-power frequency component in the bus voltage control signal output by the first control unit to obtain the target bus voltage control signal. This invention adds a notch filter unit to the PFC converter and sets its characteristic frequency at double the power frequency, enabling the notch filter unit to filter out the double-power frequency component in the bus voltage control signal output by the first control unit, outputting a signal without the double-power frequency component. This reduces the amount of bus capacitor used, allowing the on-board charger to replace electrolytic capacitors with longer-lasting and smaller film capacitors without changing its size. Therefore, it extends the service life of the on-board charger while maintaining its overall size.

Description

Technical Field

[0001] This invention relates to the field of vehicle charger technology, and more specifically, to a current processing method, a vehicle charger, and related devices. Background Technology

[0002] An on-board charger is a device installed on an electric vehicle to charge the vehicle's power battery or storage battery from the grid, or to output AC power from the power battery. Currently, most on-board chargers on the market adopt a two-stage structure, such as... Figure 1 As shown, a typical two-stage isolated on-board charger consists of two parts: a PFC (Power Factor Correction) converter and an isolated DC / DC converter. The two are connected by a bus capacitor C. bus Connected. Bus capacitor C bus The selection of the capacitor C is crucial to the control and stability of the entire system. Since the grid side is AC input and the battery side is DC output, a large amount of power at twice the power frequency will flow into the bus capacitor C. bus This causes the bus voltage to have twice the power frequency ripple superimposed on the DC voltage, such as... Figure 2 The schematic diagram shown includes bus voltage fluctuations of twice the power frequency, comprising: actual bus voltage and expected bus voltage.

[0003] In practical applications, the second harmonic fluctuation of the bus needs to be maintained within a certain range; otherwise, it will affect the overall stability of the on-board charger's control, the total harmonic distortion (THD) of the grid-side current, and even cause oscillations in the battery-side current. Therefore, a large number of electrolytic capacitors are often used as bus capacitors in the DC bus to ensure the power density of the on-board charger. However, electrolytic capacitors are not only bulky, but also experience electrolyte evaporation and increased internal resistance during operation, resulting in a shorter lifespan compared to other components in the on-board charger. This makes electrolytic capacitors a significant factor limiting the lifespan of the on-board charger.

[0004] Therefore, how to extend the service life of on-board chargers while keeping their size unchanged has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention discloses a current processing method, an on-board charger, and related devices to reduce the use of bus capacitors, so that the electrolytic capacitors of the on-board charger can be replaced with film capacitors with longer life and smaller size without affecting the original function of the on-board charger, thereby extending the service life of the on-board charger while keeping the size of the on-board charger unchanged.

[0006] A bus voltage control unit includes: a first control unit, a notch filter unit, and a power feedforward unit;

[0007] The first control unit is used to integrate the comparison result of the bus voltage sample value and the bus voltage reference value to obtain the bus voltage control signal;

[0008] The notch filter unit is used to filter out the double power frequency component in the bus voltage control signal output by the first control unit to obtain the target bus voltage control signal, wherein the characteristic frequency of the notch filter unit is set at the double power frequency.

[0009] The power feedforward unit is used to obtain the output current required by the power grid under the current load based on the battery voltage and battery current sampling signals at the current moment, and add the output current to the target bus voltage control signal output by the notch filter unit to obtain the maximum reference value of the inductor current.

[0010] Optionally, it may also include: a low-pass filter unit;

[0011] The low-pass filter unit is used to perform low-pass filtering on the bus voltage sample value to obtain the target bus voltage sample value.

[0012] Accordingly, the first control unit is used to perform integration processing on the comparison result of the target bus voltage sample value and the bus voltage reference value to obtain the bus voltage control signal.

[0013] A PFC converter includes: an inductor current control unit, a duty cycle feedforward unit, a first PWM generator, and the aforementioned bus voltage control unit;

[0014] The inductor current control unit is used to multiply the maximum reference value of the inductor current output by the bus voltage control unit with the trigonometric function of the grid in phase in the duty cycle feedforward unit to obtain the inductor current reference value, and to obtain the duty cycle correction value based on the inductor current reference value.

[0015] The duty cycle feedforward unit is used to obtain the open-loop duty cycle based on the current bus voltage value.

[0016] The first PWM generator is used to add the open-loop duty cycle output by the duty cycle feedforward unit to the duty cycle correction value output by the inductor current control unit to obtain the actual working duty cycle, and modulate the actual working duty cycle to obtain a square wave drive signal for PFC control.

[0017] Optionally, the inductor current control unit includes: a resonant control unit;

[0018] The resonant control unit is used to input the comparison value between the inductor current reference value and the inductor current sample value, and output the duty cycle correction value.

[0019] Optionally, the duty cycle feedforward unit includes: a phase-locked loop unit and a trigonometric function unit;

[0020] The phase-locked loop unit is used to obtain the current grid voltage amplitude and phase angle based on the input grid voltage sampling value;

[0021] The trigonometric function unit is used to perform trigonometric function operations on the phase angle and obtain a sine value by taking the absolute value. Based on the sine value and the bus voltage reference value, the open-loop duty cycle output by the duty cycle feedforward unit is obtained.

[0022] Optionally, the trigonometric function unit is specifically used for:

[0023] The intermediate calculation result is obtained by quoting the sine value with the bus voltage reference value.

[0024] When the phase angle is greater than 0 after trigonometric function calculation, the difference between 1 and the intermediate calculation result is determined as the open-loop duty cycle;

[0025] When the phase angle is not greater than 0 after trigonometric function calculation, the intermediate calculation result is directly determined as the open-loop duty cycle.

[0026] An on-board charger includes: an isolated DC-DC converter, the aforementioned PFC converter, and a bus capacitor connecting the isolated DC-DC converter and the PFC converter, wherein the control bandwidth of the PFC converter is greater than a preset multiple of the control bandwidth of the isolated DC-DC converter.

[0027] Optionally, the isolated DC-DC converter includes: a DC-side voltage control unit, a DC-side current control unit, a control variable feedforward unit, and a second PWM generator;

[0028] The DC-side voltage control unit is used to obtain the DC-side current reference value based on the DC-side voltage sampling value and the DC-side voltage reference value.

[0029] The DC-side current control unit is used to obtain the control variable correction value based on the DC-side current sampling value and the DC-side current reference value output by the DC-side voltage control unit;

[0030] The control variable feedforward unit is used to obtain the open-loop value of the control variable based on the bus voltage sample value, the DC voltage side sample value, the circuit parameters, and the DC current reference value output by the DC side voltage control unit.

[0031] The second PWM generator is used to add the open-loop value of the control variable output by the control variable feedforward unit and the correction value of the control variable output by the DC-side current control unit to obtain the control variable value of the isolated DC-DC converter, and modulate the control variable value of the isolated DC-DC converter to obtain a square wave drive signal for controlling the isolated DC-DC converter.

[0032] Optionally, the DC-side voltage control unit includes: a second control unit;

[0033] The second control unit is used to input the comparison result between the DC-side voltage sample value and the DC-side voltage reference value, and output the DC-side current reference value.

[0034] Optionally, the DC-side current control unit includes: a third control unit;

[0035] The third control unit is used to input the comparison result between the DC-side current sample value and the DC-side current reference value, and output the control variable correction value.

[0036] Optionally, the bus capacitor is a thin-film capacitor.

[0037] A current processing method, comprising:

[0038] The bus voltage control signal is obtained by integrating the comparison results between the bus voltage sample value and the bus voltage reference value.

[0039] The double power frequency component in the bus voltage control signal is filtered out to obtain the target bus voltage control signal.

[0040] The required output current of the power grid under the current load is obtained based on the current battery voltage and battery current sampling signals.

[0041] The maximum reference value of the inductor current is obtained by adding the output current to the target bus voltage control signal.

[0042] As can be seen from the above technical solution, the present invention discloses a current processing method, an on-board charger, and related devices. The bus voltage control unit in the on-board charger includes: a first control unit, a notch filter unit, and a power feedforward unit. The first control unit integrates the comparison results of the bus voltage sample value and the bus voltage reference value to obtain a bus voltage control signal. The notch filter unit filters out the double power frequency component in the bus voltage control signal output by the first control unit to obtain a target bus voltage control signal. The characteristic frequency of the notch filter unit is set at double the power frequency. The power feedforward unit obtains the output current required by the power grid under the current load based on the battery voltage and battery current sample signals at the current moment. The output current is added to the target bus voltage control signal output by the notch filter unit to obtain the maximum reference value of the inductor current. By adding a notch filter unit in the PFC converter and setting the characteristic frequency of the notch filter unit at double the power frequency, it is equivalent to adding a large gain attenuation at double the power frequency, so that the notch filter unit can filter out the double power frequency component in the bus voltage control signal output by the first control unit, and finally output a signal without the double power frequency component. This reduces the use of bus capacitors, allowing the electrolytic capacitors in the vehicle charger to be replaced with longer-lasting and smaller film capacitors without affecting the original function of the vehicle charger, thus extending the service life of the vehicle charger while keeping its size unchanged. Attached Figure Description

[0043] 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 published drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of an existing two-stage isolated vehicle charger;

[0045] Figure 2 This is a schematic diagram of an existing bus voltage with fluctuations at twice the power frequency.

[0046] Figure 3 This is a schematic diagram of the control loop of a bus voltage control unit disclosed in an embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of a PFC control loop disclosed in an embodiment of the present invention;

[0048] Figure 5 This is a schematic diagram of the structure of a vehicle charger disclosed in an embodiment of the present invention;

[0049] Figure 6 This is a schematic diagram of the control loop of an isolated DC-DC converter disclosed in an embodiment of the present invention;

[0050] Figure 7 This is a flowchart of a current processing method disclosed in an embodiment of the present invention;

[0051] Figure 8 This is a circuit diagram of a vehicle charger disclosed in an embodiment of the present invention;

[0052] Figure 9(a) is a waveform diagram of a PFC converter using a 2mF bus capacitor and a common control loop disclosed in an embodiment of the present invention.

[0053] Figure 9(b) is a waveform diagram of the PFC converter using a 500uF bus capacitor and a common control loop disclosed in an embodiment of the present invention.

[0054] Figure 10 This is a simulation diagram of the control effect of a PFC control loop disclosed in an embodiment of the present invention;

[0055] Figure 11 This is a simulation diagram of the control effect of another PFC control loop disclosed in an embodiment of the present invention;

[0056] Figure 12 This is a simulation diagram of the control effect of an isolated DC-DC converter control loop disclosed in an embodiment of the present invention. Detailed Implementation

[0057] 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.

[0058] This invention discloses a current processing method, an on-board charger, and related devices. By adding a notch filter unit to the PFC converter and setting the characteristic frequency of the notch filter unit at twice the power frequency, which is equivalent to adding a large gain attenuation at twice the power frequency, the notch filter unit can filter out the twice-power frequency component in the bus voltage control signal output by the first control unit, and finally output a signal without the twice-power frequency component. This reduces the use of bus capacitors, allowing the on-board charger to replace electrolytic capacitors with longer-lasting and smaller film capacitors without affecting the original function of the on-board charger, while maintaining the same size. Therefore, it extends the service life of the on-board charger while keeping its size unchanged.

[0059] First, it should be noted that the following conclusions were reached through derivation:

[0060] Battery charging power P o Bus voltage V bus Busbar capacitance C bus Bus voltage fluctuation ΔV bus The relationship between the power grid frequency f and the power grid frequency is shown in formula (1), which is as follows:

[0061]

[0062] If the bus capacity C bus If reduced to one-third of its original size, the bus voltage V bus The fluctuation will become three times the original value. Therefore, the control of the on-board charger is based on the condition that there is a large fluctuation of twice the power frequency on the bus.

[0063] (1) Keep the grid-side current THD within the normal level (5%);

[0064] (2) Ensure that the battery side outputs a non-oscillating DC charging current.

[0065] Based on this, see Figure 3 This invention discloses a schematic diagram of the control loop of a bus voltage control unit. In this embodiment, the bus voltage control unit is applied to a PFC converter. The bus voltage control unit includes: a first control unit 11, a notch filter unit 12, and a power feedforward unit 13.

[0066] The first control unit 11 is used to sample the bus voltage value V. bus and bus voltage reference value V bus_ref The comparison results are integrated to obtain the bus voltage control signal.

[0067] Preferably, the first control unit 11 can be a first PI control unit, but other control units that can perform this function are also feasible, and no specific limitation is made here.

[0068] Specifically, the bus voltage reference value V bus_ref Subtract the bus voltage sampling value V bus The comparison results of the two were obtained.

[0069] The notch filter unit 12 is used to filter out the double power frequency component in the bus voltage control signal output by the first control unit 11 to obtain the target bus voltage control signal, wherein the characteristic frequency of the notch filter unit 12 is set at the double power frequency.

[0070] Typically, the bus voltage sampling value V busThe signal contains a large amount of double power frequency components, which are fed back into the bus voltage control signal output by the first control unit 11. Therefore, this invention adds a notch filter unit 12 after the first control unit 11 and sets the characteristic frequency of the notch filter unit 12 at the double power frequency. This is equivalent to adding a large gain attenuation at the double power frequency, and this gain attenuation does not affect the overall control bandwidth of the PFC converter, thereby filtering out the double power frequency components in the bus voltage control signal output by the first control unit 11.

[0071] The power feedforward unit 13 is used to obtain the output current required by the power grid under the current load based on the battery voltage and battery current sampling signals at the current moment, and add the output current to the target bus voltage control signal output by the notch filter unit 12 to obtain the maximum reference value of the inductor current.

[0072] The voltage loop bandwidth of the bus voltage control unit is usually designed to be low, and the notch filter unit 12 will have an additional impact on the voltage loop dynamics. Therefore, a power feedforward unit 13 is added. The power feedforward unit 13 obtains the output current required by the grid under the current load based on the battery voltage and battery current sampling signals at the current moment. By adding the output power to the target bus voltage control signal output by the notch filter unit 12, the maximum reference value of the inductor current output by the bus voltage control unit is obtained.

[0073] In summary, the present invention discloses a bus voltage control unit, comprising: a first control unit 11, a notch filter unit 12, and a power feedforward unit 13. The first control unit 11 integrates the comparison results of the bus voltage sample value and the bus voltage reference value to obtain a bus voltage control signal. The notch filter unit 12 filters out the double power frequency component in the bus voltage control signal output by the first control unit 11 to obtain a target bus voltage control signal. The characteristic frequency of the notch filter unit 12 is set at the double power frequency. The power feedforward unit 13 obtains the output current required by the power grid under the current load based on the battery voltage and battery current sample signals at the current moment, and adds the output current to the target bus voltage control signal output by the notch filter unit 12 to obtain the maximum reference value of the inductor current. This invention adds a notch filter unit 12 to the PFC converter, setting the characteristic frequency of the notch filter unit 12 at twice the power frequency. This effectively adds a significant gain attenuation at twice the power frequency, allowing the notch filter unit 12 to filter out the twice-power frequency component in the bus voltage control signal output by the first control unit 11, ultimately outputting a signal free of the twice-power frequency component. This reduces the amount of bus capacitor used, allowing the on-board charger to replace electrolytic capacitors with longer-lasting, smaller film capacitors without affecting its original functionality, while maintaining the same size. Therefore, it extends the lifespan of the on-board charger while keeping its size unchanged.

[0074] To further optimize the above embodiments, the bus voltage control unit may further include: a low-pass filter unit 14;

[0075] Low-pass filter unit 14 is used to sample the bus voltage value V. bus The target bus voltage sample value is obtained by performing low-pass filtering;

[0076] Accordingly, the first control unit 11 is used to sample the target bus voltage value and the bus voltage reference value V. bus_ref The comparison results are integrated to obtain the bus voltage control signal.

[0077] In this embodiment, the bus voltage sampling value V is obtained through the low-pass filter unit 14. bus Low-pass filtering can filter out the bus voltage sample value V. bus The second power frequency component is partially filtered out by the notch filter unit 12, and the remaining second power frequency component is then filtered out.

[0078] Corresponding to the above embodiments, the present invention also discloses a PFC converter.

[0079] See Figure 4 The present invention discloses a schematic diagram of a PFC control loop. The PFC converter includes: a bus voltage control unit 10, an inductor current control unit 20, a duty cycle feedforward unit 30, and a first PWM (Pulse Width Modulation) generator 40.

[0080] The inductor current control unit 20 is used to multiply the maximum reference value of the inductor current output by the bus voltage control unit 10 by the trigonometric function of the grid in phase in the duty cycle feedforward unit 30 to obtain the inductor current reference value I. L_ref And based on the inductor current reference value I L_ref Obtain the duty cycle correction value.

[0081] The duty cycle feedforward unit 30 is used to obtain the open-loop duty cycle based on the current bus voltage value.

[0082] The first PWM generator 40 is used to add the open-loop duty cycle output by the duty cycle feedforward unit 30 to the duty cycle correction value output by the inductor current control unit 20 to obtain the actual working duty cycle, and then modulate the actual working duty cycle to obtain a square wave drive signal for PFC control.

[0083] In practical applications, the actual operating duty cycle can be used as the control variable value of the PFC converter and compared with the triangular carrier wave to obtain the square wave drive signal for PFC control.

[0084] To further optimize the above embodiments, the inductor current control unit 20 may include: a resonant control unit 21;

[0085] The resonant control unit 21 is used to input the inductor current reference value I. L_ref With the inductor current sampling value i L The comparison value is used to output the duty cycle correction value.

[0086] Preferably, the resonant control unit 21 can be a PIR (Proportional Integral Resonance) control unit. However, other control units capable of performing this function are also feasible, and no specific limitation is made here.

[0087] In other words, the inductor current reference value I L_ref With the inductor current sampling value i L The comparison value is then input into the resonant control unit 21, which processes the comparison value to obtain the duty cycle correction value.

[0088] To further optimize the above embodiments, the duty cycle feedforward unit 30 may include: a phase-locked loop unit 31 and a trigonometric function unit 32;

[0089] Phase-locked loop unit 31 is used to obtain the current grid voltage amplitude and phase angle based on the input grid voltage sampling value;

[0090] The trigonometric function unit 32 is used to perform trigonometric function operations on the phase angle and obtain a sine value by taking the absolute value. Based on the sine value and the bus voltage reference value, the open-loop duty cycle output by the duty cycle feedforward unit 30 is obtained.

[0091] The implementation process of duty cycle feedforward unit 30 is as follows:

[0092] Grid voltage sampling value V g After calculation by phase-locked loop unit 31, the amplitude V of the current grid voltage is obtained. ac_amp And the phase angle φ; the phase angle φ is obtained by taking the absolute value of the trigonometric function sin operation, and the sine value is based on this sine value and the bus voltage reference value V. bus_ref The open-loop duty cycle of the duty cycle feedforward unit 30 is obtained.

[0093] Specifically, trigonometric function unit 32 can be used for:

[0094] The intermediate calculation result is obtained by quoting the sine value with the bus voltage reference value.

[0095] When the phase angle is greater than 0 after trigonometric function calculation, the difference between 1 and the intermediate calculation result is determined as the open-loop duty cycle;

[0096] When the phase angle is not greater than 0 after trigonometric function calculation, the intermediate calculation result is directly determined as the open-loop duty cycle.

[0097] Specifically, the sine value obtained by taking the absolute value of the phase angle φ after performing a trigonometric function sin operation is compared with the bus voltage reference value V. bus_ref Dividing yields the intermediate calculation result |V ac_amp *sin(φ)| / V bus_ref If sin(φ) > 0, then use 1 - |V ac_amp *sin(φ)| / V bus_ref The open-loop duty cycle is used as the output of the duty cycle feedforward unit 30; otherwise, it is |V ac_amp *sin(φ)| / V bus_ref The open-loop duty cycle is the output of the duty cycle feedforward unit 30.

[0098] Corresponding to the above method embodiments, the present invention also discloses an on-board charger.

[0099] See Figure 5 The present invention discloses a schematic diagram of the structure of a vehicle charger, which includes: an isolated DC-DC converter, Figure 4 The PFC converter in the illustrated embodiment, and the bus capacitor connecting the isolated DC converter and the PFC converter.

[0100] The control bandwidth of the PFC converter is greater than a preset multiple of the control bandwidth of the isolated DC converter. The value of the preset multiple depends on the actual needs, such as 5 times. This invention does not limit this value.

[0101] It should be noted that the function of the PFC converter is to control the power factor and total harmonic distortion (THD) of the grid-side current. The function of the isolated DC-DC converter is to control the voltage and current at the battery terminals. Furthermore, the isolated DC-DC converter maintains the bus voltage at a given reference value V, as achieved by the PFC converter. bus_ref Only then did I start working.

[0102] The key design elements of the PFC converter in this invention are the notch filter unit 12 and the control bandwidth. Since a significant double-frequency component will be reflected in the output of the first control unit 11, designing the bandwidth of the first control unit 11 to be very low would have some control effect on the double-frequency component. However, considering that the bus bears all the double-frequency fluctuations, to avoid the difficulty in designing the control loop of the isolated DC-DC converter due to the low control bandwidth of the PFC converter, this invention designs the control bandwidth of the PFC converter to be greater than a preset multiple of the control bandwidth of the isolated DC-DC converter, which is at least 5 times. Simultaneously, this invention adds a notch filter unit 12 after the first control unit 11, and sets the characteristic frequency of the notch filter unit 12 at the double-frequency position. This is equivalent to adding a large gain attenuation at the double-frequency position, and this gain attenuation does not affect the overall control bandwidth of the PFC converter, thus filtering out the double-frequency component in the bus voltage control signal output by the first control unit 11.

[0103] The key to designing an isolated DC-DC converter is that its control bandwidth should be much smaller than that of a PFC converter. This ensures that the isolated DC-DC converter has greater equivalent damping at twice the power frequency, reducing its response to fluctuations at twice the power frequency of the bus. Because of the relatively low control bandwidth of the isolated DC-DC converter, feedforward calculations of the control inputs can effectively improve its dynamic response.

[0104] In summary, this invention discloses an on-board charger. By adding a notch filter unit 12 to the PFC converter and setting the characteristic frequency of the notch filter unit 12 at twice the power frequency, which is equivalent to adding a large gain attenuation at twice the power frequency, the notch filter unit 12 can filter out the twice-power frequency component in the bus voltage control signal output by the first control unit 11, and finally output a signal without the twice-power frequency component. At the same time, by setting the control bandwidth of the PFC converter to be greater than a preset multiple of the control bandwidth of the isolated DC converter, the isolated DC converter has a large equivalent damping at twice the power frequency, thereby reducing the response to twice-power frequency fluctuations. This further reduces the twice-power frequency fluctuations of the bus voltage, thereby reducing the use of bus capacitors. This allows the on-board charger to replace electrolytic capacitors with longer-lasting and smaller film capacitors without affecting the original function of the on-board charger, while maintaining the same size. Therefore, it extends the service life of the on-board charger while keeping the size of the on-board charger unchanged.

[0105] Based on the above discussion, it can be concluded that Figure 5 The bus capacitor in the illustrated embodiment can be significantly reduced compared to existing technologies, for example, Figure 5 Bus capacitance < C bus / 3 Therefore, in this embodiment, the bus capacitor can preferably be a thin-film capacitor with a longer lifespan and smaller size.

[0106] To further optimize the above embodiments, see [link to relevant documentation]. Figure 6 The present invention discloses a control loop diagram of an isolated DC-DC converter. The isolated DC-DC converter includes: a DC-side voltage control unit 50, a DC-side current control unit 60, a control variable feedforward unit 70, and a second PWM generator 80.

[0107] The DC-side voltage control unit 50 is used to measure the DC-side voltage sampling value V. dc and DC side voltage reference value V dc_ref Obtain the DC side current reference value I dc_ref .

[0108] DC-side current control unit 60, used to measure DC-side current sampling value i dc and the DC side current reference value I output by the DC side voltage control unit 50 dc_ref The corrected values ​​of the control variables are obtained.

[0109] Among them, the control variables in the control variable correction value vary depending on the control method, and may be phase shift angle, frequency, etc.

[0110] The control variable feedforward unit 70 is used to control the bus voltage sample value V. bus DC voltage side sampling value V dc Circuit parameters and DC-side current reference value I output by DC-side voltage control unit 50 dc_ref This yields the open-loop values ​​of the control variables.

[0111] Among them, the control variables in the open-loop control variables can be phase shift angle, frequency, etc.

[0112] The second PWM generator 80 is used to add the open-loop value of the control variable output by the control variable feedforward unit 70 and the correction value of the control variable output by the DC side current control unit 60 to obtain the control variable value of the isolated DC converter, and modulate the control variable value of the isolated DC converter to obtain a square wave drive signal for controlling the isolated DC converter.

[0113] In practical applications, the control variable values ​​of the isolated DC-DC converter can be compared with a triangular carrier wave to obtain a square wave drive signal for controlling the isolated DC-DC converter.

[0114] To further optimize the above embodiments, the DC-side voltage control unit 50 may include: a second control unit 51;

[0115] The second control unit 51 is used to input the DC side voltage sampling value V.dc and DC side voltage reference value V dc_ref The comparison results output the DC side current reference value I. dc_ref .

[0116] In other words, the DC side voltage sampling value V dc and DC side voltage reference value V dc_ref After comparison, the DC side current reference value I is obtained by the second control unit 51. dc_ref .

[0117] To further optimize the above embodiments, the DC-side current control unit 60 may include: a third control unit 61;

[0118] The third control unit 61 is used to input the DC side current sampling value i. dc and DC side current reference value I dc_ref The comparison results are used to output the corrected values ​​of the control variables.

[0119] In other words, the DC side current sampling value i dc and DC side current reference value I dc_ref After comparison, the corrected value of the control variable is obtained through the third control unit 61.

[0120] Corresponding to the above embodiments, the present invention also discloses a current processing method.

[0121] See Figure 7 The present invention discloses a flowchart of a current processing method, which is similar to... Figure 3 Corresponding to the illustrated embodiment, the method includes:

[0122] Step S101: Integrate the comparison results of the bus voltage sample value and the bus voltage reference value to obtain the bus voltage control signal;

[0123] Step S102: Filter out the double power frequency component in the bus voltage control signal to obtain the target bus voltage control signal;

[0124] Step S103: Obtain the output current required by the power grid under the current load based on the current battery voltage and battery current sampling signals;

[0125] Step S104: Add the output current to the target bus voltage control signal to obtain the maximum reference value of the inductor current.

[0126] In summary, this invention discloses a current processing method that filters out the double power frequency component in the bus voltage control signal, resulting in a final output signal free of the double power frequency component. This reduces the use of bus capacitors, allowing the on-board charger to replace electrolytic capacitors with longer-lasting and smaller film capacitors without affecting its original functions, while maintaining the same size. Thus, it extends the service life of the on-board charger while keeping its size unchanged.

[0127] To verify that the solution disclosed in this invention can filter out twice the power frequency component, thereby effectively reducing the use of bus capacitors, please refer to [link to relevant documentation]. Figure 8 The present invention discloses a circuit diagram of a vehicle charger, wherein Filter in the diagram represents a filter.

[0128] Assume the maximum charging power is 3300W, the grid frequency is 50Hz, and the bus voltage is 400V. If it is necessary to maintain the bus voltage fluctuation at 3% of the bus voltage (400±6V), then the required bus capacitance can be calculated as 2mF according to formula (1).

[0129] The capacitance is reduced to 25% of its original value, or 500uF. Given that the volume of an electrolytic capacitor is three times that of a film capacitor for the same capacitance, using a film capacitor would result in a smaller overall volume compared to an electrolytic capacitor. With a 500uF bus capacitor, if the second harmonic power fluctuation is entirely borne by the bus capacitor, the second harmonic fluctuation of the bus voltage will reach ±24V. Figures 9(a) and 9(b) show the PFC operation using a common closed-loop controller circuit with different capacitors; the upper value is the bus voltage, and the lower value is the grid-side current. It can be seen that when a smaller bus capacitor is used, the bus voltage fluctuates significantly, causing severe distortion of the grid-side current.

[0130] The severe distortion of the grid-side current is due to the intense second harmonic fluctuations of the bus being reflected in the current reference value through the controller. This is because the control bandwidth of the PFC converter is large, and the corrective action of the controller alone cannot eliminate such fluctuations.

[0131] Figure 10 The diagram shows a comparison of the PFC converter's operation using a common closed-loop controller and the controller loop of this invention. The top represents the bus voltage, and the bottom represents the grid current. The area before the dashed line uses the common PFC control loop, while the area after the dashed line switches to the PFC control loop of this invention.

[0132] Depend on Figure 10 As can be seen, the PFC control loop proposed in this invention (see details) Figure 4Even under severe bus voltage fluctuations, low THD control of grid-side current can still be achieved, effectively suppressing the impact of severe second harmonic fluctuations in the bus.

[0133] Figure 11 The diagram shows the power factor control before and after switching the control loop; the top represents the grid voltage, and the bottom represents the grid current. Simulation results... Figure 11 It can be seen that the PFC control loop proposed in this invention corrects the grid-side THD without affecting the grid-side power factor control.

[0134] Figure 12 The figure shows the bus voltage and ISO_DCDC battery-side voltage and current waveforms using the ISO_DCDC control loop proposed in this invention. As can be seen from the figure, under fluctuating bus voltage conditions, the battery charging current contains almost no second-harmonic component, and the second-harmonic power fluctuations are absorbed by the bus capacitor as intended.

[0135] In summary, the two-stage isolated vehicle charger with control loop proposed in this invention effectively reduces bus capacitance and achieves the intended function.

[0136] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover 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 limitations, 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.

[0137] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0138] 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 bus voltage control unit, characterized in that, Applied to PFC converters, including: first control unit, notch filter unit and power feedforward unit; The first control unit is used to integrate the comparison result of the bus voltage sample value and the bus voltage reference value to obtain the bus voltage control signal; The notch filter unit is used to filter out the double power frequency component in the bus voltage control signal output by the first control unit to obtain the target bus voltage control signal, wherein the characteristic frequency of the notch filter unit is set at the double power frequency. The power feedforward unit is used to obtain the output current required by the power grid under the current load based on the battery voltage and battery current sampling signals at the current moment, and add the output current to the target bus voltage control signal output by the notch filter unit to obtain the maximum reference value of the inductor current.

2. The bus voltage control unit according to claim 1, characterized in that, Also includes: Low-pass filter unit; The low-pass filter unit is used to perform low-pass filtering on the bus voltage sample value to obtain the target bus voltage sample value. Accordingly, the first control unit is used to perform integration processing on the comparison result of the target bus voltage sample value and the bus voltage reference value to obtain the bus voltage control signal.

3. A PFC converter, characterized in that, include: The inductor current control unit, the duty cycle feedforward unit, the first PWM generator, and the bus voltage control unit as described in claim 1; The inductor current control unit is used to multiply the maximum reference value of the inductor current output by the bus voltage control unit with the trigonometric function of the grid in phase in the duty cycle feedforward unit to obtain the inductor current reference value, and to obtain the duty cycle correction value based on the inductor current reference value. The duty cycle feedforward unit is used to obtain the open-loop duty cycle based on the current bus voltage value. The first PWM generator is used to add the open-loop duty cycle output by the duty cycle feedforward unit to the duty cycle correction value output by the inductor current control unit to obtain the actual working duty cycle, and modulate the actual working duty cycle to obtain a square wave drive signal for PFC control.

4. The PFC converter according to claim 3, characterized in that, The inductor current control unit includes: a resonant control unit; The resonant control unit is used to input the comparison value between the inductor current reference value and the inductor current sample value, and output the duty cycle correction value.

5. The PFC converter according to claim 3, characterized in that, The duty cycle feedforward unit includes: a phase-locked loop unit and a trigonometric function unit; The phase-locked loop unit is used to obtain the current grid voltage amplitude and phase angle based on the input grid voltage sampling value; The trigonometric function unit is used to perform trigonometric function operations on the phase angle and obtain a sine value by taking the absolute value. Based on the sine value and the bus voltage reference value, the open-loop duty cycle output by the duty cycle feedforward unit is obtained.

6. The PFC converter according to claim 5, characterized in that, The trigonometric function unit is specifically used for: The intermediate calculation result is obtained by quoting the sine value with the bus voltage reference value. When the phase angle is greater than 0 after trigonometric function calculation, the difference between 1 and the intermediate calculation result is determined as the open-loop duty cycle; When the phase angle is not greater than 0 after trigonometric function calculation, the intermediate calculation result is directly determined as the open-loop duty cycle.

7. A vehicle charger, characterized in that, include: An isolated DC-DC converter, a PFC converter according to any one of claims 3 to 6, and a bus capacitor connecting the isolated DC-DC converter and the PFC converter, wherein the control bandwidth of the PFC converter is greater than a preset multiple of the control bandwidth of the isolated DC-DC converter.

8. The vehicle charger according to claim 7, characterized in that, The isolated DC-DC converter includes: a DC-side voltage control unit, a DC-side current control unit, a control variable feedforward unit, and a second PWM generator; The DC-side voltage control unit is used to obtain the DC-side current reference value based on the DC-side voltage sampling value and the DC-side voltage reference value. The DC-side current control unit is used to obtain the control variable correction value based on the DC-side current sampling value and the DC-side current reference value output by the DC-side voltage control unit; The control variable feedforward unit is used to obtain the open-loop value of the control variable based on the bus voltage sample value, the DC voltage side sample value, the circuit parameters, and the DC current reference value output by the DC side voltage control unit. The second PWM generator is used to add the open-loop value of the control variable output by the control variable feedforward unit and the correction value of the control variable output by the DC-side current control unit to obtain the control variable value of the isolated DC-DC converter, and modulate the control variable value of the isolated DC-DC converter to obtain a square wave drive signal for controlling the isolated DC-DC converter.

9. The vehicle charger according to claim 8, characterized in that, The DC-side voltage control unit includes: a second control unit; The second control unit is used to input the comparison result between the DC-side voltage sample value and the DC-side voltage reference value, and output the DC-side current reference value.

10. The vehicle charger according to claim 8, characterized in that, The DC-side current control unit includes: a third control unit; The third control unit is used to input the comparison result between the DC-side current sample value and the DC-side current reference value, and output the control variable correction value.

11. The vehicle charger according to claim 7, characterized in that, The bus capacitor is a thin-film capacitor.

12. A current processing method, characterized in that, Applied to PFC converters, including: The bus voltage control signal is obtained by integrating the comparison results between the bus voltage sample value and the bus voltage reference value. The double power frequency component in the bus voltage control signal is filtered out to obtain the target bus voltage control signal. The required output current of the power grid under the current load is obtained based on the current battery voltage and battery current sampling signals. The maximum reference value of the inductor current is obtained by adding the output current to the target bus voltage control signal.

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