A loss analysis method of a charging pile circuit

Abstract

The present application relates to a kind of loss analysis method of charging pile circuit.First, the characteristics of a kind of charging pile circuit are analyzed, then according to its characteristics, the loss model of two stages is established, respectively, the VIENNA rectification loss model of front stage and the DC / DC isolation loss model of rear stage.The front stage circuit is PFC network, and its loss includes three parts, respectively, the conduction loss of power device, the switching loss of power device and the loss of passive device;The rear stage circuit is divided into switching network, compensation network and rectification filter network, the switching network includes the conduction loss and the turn-off loss of switch tube, the compensation network includes the loss of resonant inductance, and the rectification filter network includes the core loss of transformer, the winding loss of transformer and the loss of rectification diode, finally, the running condition of existing circuit is judged through loss calculation prediction formula.The present application can accurately calculate the loss of such charging pile circuit, judge the performance of charging pile, and predict the fault state of charging pile.

Description

Technical Field

[0001] The present invention relates to the technical field of charging pile analysis, and more specifically, to a loss analysis method for a charging pile circuit. Background Art

[0002] Current charging piles obtain power from the grid and ultimately transmit it to the user. This energy transfer process results in energy loss, specifically losses within the charging pile's internal circuits. Rectifiers are a key component in transferring energy from the grid to the user. Currently, most commonly used rectifiers utilize diode uncontrolled rectifier circuits and thyristor phase-controlled rectifier circuits. While these rectifiers offer a degree of cost-effectiveness and reliability for charging piles due to their low circuit complexity, they can also negatively impact grid-side current quality, such as severe waveform distortion, low power factor, and high output voltage ripple.

[0003] Current charging piles are powered by a dedicated transformer or multiple distribution boxes. The charging pile receives power from the grid and ultimately transmits it to the user. This energy transfer process results in energy loss, specifically circuit losses within the charging pile. When the charging pile is operating normally, its losses should remain stable within a certain range. If the losses exceed this range, it may indicate a circuit failure within the charging pile.

[0004] The current loss analysis of charging piles is generally to subtract the total output power from the total input power. It cannot reflect in real time whether the loss of the charging pile is abnormal, and it cannot accurately locate the specific fault part in the charging pile to carry out precise operation and maintenance of the charging pile. Summary of the Invention

[0005] The purpose of the present invention is to provide a loss analysis method for a charging pile circuit, which can accurately calculate the loss of the charging pile circuit, judge the performance of the charging pile based on the loss relationship, and predict the fault state of the charging pile.

[0006] To achieve the above objectives, the technical solution of the present invention is: a method for analyzing the loss of a charging pile circuit, first performing a characteristic analysis on a charging pile circuit; then establishing two-stage loss models based on its characteristics, namely a front-stage VIENNA rectifier loss model and a rear-stage DC / DC isolation loss model; and finally determining the operating status of the charging pile circuit using a loss calculation prediction formula. The front-stage circuit is a PFC network, whose losses consist of three parts: power device conduction loss, power device switching loss, and passive device loss; the rear-stage circuit is divided into a switching network, a compensation network, and a rectifier and filter network. The switching network includes switch tube conduction loss and turn-off loss, the compensation network includes resonant inductor loss, and the rectifier and filter network includes transformer core loss, transformer winding loss, and rectifier diode loss.

[0007] Compared with the prior art, the present invention has the following beneficial effects:

[0008] 1. The present invention introduces a loss coefficient, and the loss model is not limited to the case of an ambient temperature of 25°C, and the loss calculation is more accurate.

[0009] 2. The present invention is directed to a charging pile circuit and may not be applicable to other circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a schematic diagram of the charging pile circuit of the present invention.

[0011] Figure 2 This is a block diagram of the loss analysis principle of the present invention. DETAILED DESCRIPTION

[0012] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0013] like Figure 1 As shown, the charging pile circuit consists of a front stage and a back stage, with the left input terminal connected to the mains and the right output terminal connected to the power battery. The present invention provides a loss analysis method for a charging pile circuit, comprising the following steps:

[0014] Step S1: First Figure 1 The charging pile circuit in the Figure 2 The front and rear two-stage loss models shown are the front-stage VIENNA rectification loss model and the rear-stage DC / DC isolation loss model, respectively, denoted as P i and P d The front-stage circuit is a PFC network, and the back-stage circuit is divided into a switch network, a compensation network, and a rectifier filter network;

[0015] Step S2: Analyze the characteristics of each network to obtain the corresponding loss type. The PFC network contains three losses: power device conduction loss, power device switching loss and passive device loss, which are respectively denoted as P i1 、P i2 、P i3 ; The switching network includes MOSFET conduction loss and MOSFET turn-off loss, denoted as P ON 、P S ; The compensation network includes the resonant inductor loss, denoted as P cw The rectifier filter network includes transformer loss and rectifier diode loss, which are denoted as P Tw 、P CD .

[0016] The following steps will be combined Figure 1 The components are described below.

[0017] Step S3: Using the conduction loss calculation method, assuming that the switching frequency of the power semiconductor device is high enough, the entire power frequency cycle is divided into a sufficient number of switching cycle time intervals, and then the loss at a given moment is multiplied by the duty cycle and the switching frequency, and the average conduction loss is calculated by integration over one power frequency cycle.

[0018] Step S4: According to the method described in step S3, combined with the on-state VI (voltage-current) characteristics of the power semiconductor device, the conduction loss expression of the IGBT (S1-S6) can be obtained:

[0019]

[0020] Where V CE0 is the saturation voltage; R0 is the on-state resistance; I Cavg , I Crms are the average current and effective current flowing through the IGBT respectively.

[0021] Step S5: Similarly, the fast recovery diode (D F1 -D F6 ) and thyristor (D W1 -D W6 ) are as follows:

[0022]

[0023]

[0024] Where V FD0 , R FD0 are the saturation voltage and on-state resistance of the fast recovery diode, I Davg , I Drms is the average value and effective value of the current flowing through the fast recovery diode; V DW0 , R DW0 are the saturation voltage and on-state resistance of the thyristor, I Wavg , I Wrms is the average value and effective value of the current flowing through the thyristor.

[0025] Therefore, the conduction loss of the switching device in the previous circuit can be obtained:

[0026] P i1 =P S,con +P FD,con +P DW,con

[0027] Step S6: The switching energy-current (E sw—I) characteristic curve is fitted to calculate. This method reveals that the switching loss of power devices is proportional to the breaking voltage and current, and is verified by the data model of power devices.

[0028] Step S7: According to the method described in step S6, combined with the energy loss characteristic curves of the IGBT (S1-S6) when it is turned on and off, the IGBT switching loss expression can be obtained:

[0029]

[0030] Where, and They represent the average turn-on energy loss and average turn-off energy loss of IGBT, respectively. sw Indicates the switching frequency.

[0031] Step S8: Similarly, a fast recovery diode (D F1 -D F6 )’s reverse recovery loss:

[0032] P D,rec =E D,rec f sw

[0033] Where E D,rec represents the fast recovery diode voltage, f sw Indicates the switching frequency.

[0034] Therefore, the switching loss of the switching device in the previous circuit can be obtained:

[0035] P i2 =P sw +P D,rec

[0036] Step S9: Passive device loss is mainly caused by inductance (L1-L6, L g1 -L g3 ) loss and capacitance (C f1 -C f3 ) loss, and the Steinmetz equation combined with the core loss curve of the amorphous alloy core can be used to obtain the inductor loss expression:

[0037]

[0038] Where P core is the core loss, W Fe is the core weight, ρ cu Resistivity, l L Indicates length, A W Represents the cross-sectional area; I L,rms is the effective value of the inductor current.

[0039] Step S10: Similarly, the filter capacitor (C f1 -C f3 ) loss calculation expression is:

[0040]

[0041] Where, I C,rms is the effective value of the current flowing through the capacitor, R C,ESR is the equivalent series resistance of the filter capacitor.

[0042] Therefore, the passive device loss of the switching device in the previous stage circuit can be obtained:

[0043] P i3 =P L +P C

[0044] The above steps can be used to obtain the front-stage VIENNA rectification loss model loss:

[0045] P i =P i1 +P i2 +P i3

[0046] Step S11: According to the LLC resonant characteristics of the compensation network, the MOS tubes (M1 to M4) in the switch network are turned on at zero voltage, and only the conduction loss P needs to be calculated. ON and turn-off loss P S Since the current flowing through M1 to M4 can be equivalent to a sine wave, assuming that LLC works at a resistive point, the effective value of the current flowing through a single switch tube can be obtained as I rms_s1 , we get the power loss formula:

[0047] P ON =(I rms_s1 ) 2 ×R DS

[0048] where R DS is the on-resistance.

[0049] According to the turn-off transient process of the switch tube, the turn-off loss formula of the switch tube is:

[0050]

[0051] V in_max is the maximum voltage when turned off, I off is the maximum current when shutting down, f s_max is the maximum operating frequency of the circuit, t p is the voltage rise time when turning off, t s is the current fall time when turning off.

[0052] Step S12: Known resonance parameter L r The value of , and then design the inductance according to the AP method, calculate the winding AC resistance R act , the copper loss P of the resonant inductor can be obtained cu , iron loss P fe The coefficient K can be obtained by fitting the relationship curve between core loss and magnetic flux density based on the resonant frequency and the specific materials used. c , α, β, and finally calculate the resonant inductance L in the compensation network r The loss of V c is the core volume, resonant capacitance C r The loss can be ignored, and the specific formula is as follows:

[0053]

[0054] Step S13: Calculate the transformer (T1, T2) winding loss in the rectifier filter network. Calculate the primary and secondary winding AC resistance R according to the maximum power of the transformer. dctp 、R dcts , combined with the transformer current effective value i rm , we get the winding loss formula P w as follows:

[0055] P w =P wp +P ws =(R dctp +R dcts )×i rm 2

[0056] Step S14, the calculation method of the transformer core loss is the same as step S12, and the total power loss of the transformer can be obtained as:

[0057]

[0058] Step S15: Calculate the loss P of the rectifier diodes (D1-D8) CD .

[0059]

[0060] Among them I F is the average forward current, V F is the forward voltage, which can be fitted according to the data sheet of the specific diode.

[0061] The post-stage DC / DC isolation loss model can be obtained from steps S11-S15:

[0062] P d =P ON +PS +P cw +P Tw +P CD

[0063] Step S16: Introducing loss coefficient w i 、w j According to the experimental data, the loss curve based on 25℃ is fitted to obtain w i and w j , we get the loss calculation prediction formula:

[0064] P all =w i P i +w j P d

[0065] Step S17: The percentage of power loss calculated from the power loss model to actual power consumption indicates the charging pile's operating efficiency. If this efficiency meets the specific design requirements, the charging pile's performance is considered optimal. If the actual operating efficiency of the charging pile far exceeds the model's calculated value, the charging pile is considered abnormal, indicating a circuit fault.

[0066] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions and effects do not exceed the scope of the technical solution of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A method for analyzing the loss of a charging pile circuit, characterized in that: First, a charging pile circuit characteristic analysis is performed. Then, based on its characteristics, two-stage loss models are established: a front-stage VIENNA rectification loss model and a rear-stage DC / DC isolation loss model. Finally, the operating status of the charging pile circuit is determined using a loss calculation prediction formula. The method includes the following steps: Step S1: First, analyze the characteristics of a charging pile circuit, and then establish the front and rear two-stage loss models, namely the front-stage VIENNA rectification loss model and the rear-stage DC / DC isolation loss model, and record them as P i and P d The front-stage circuit of the charging pile circuit is the PFC network, and the back-stage circuit of the charging pile circuit is divided into a switching network, a compensation network, and a rectifier filter network. Step S2: Analyze the characteristics of each network to obtain the corresponding loss type; the PFC network contains three losses: power device conduction loss, power device switching loss and passive device loss, which are respectively denoted as P i1 、P i2 、P i3 ; The switching network includes MOSFET conduction loss and MOSFET turn-off loss, denoted as P ON 、P S ; The compensation network includes the resonant inductor loss, denoted as P cw The rectifier filter network includes transformer loss and rectifier diode loss, which are denoted as P Tw 、P CD ; Step S3: Using the conduction loss calculation method, assuming that the switching frequency of the power semiconductor device is high enough, the entire power frequency cycle is divided into multiple switching cycle time intervals, and then the loss at a given moment is multiplied by the duty cycle and the switching frequency, and the average conduction loss is calculated by integration over one power frequency cycle. Specifically, the conduction loss expression of the IGBT is obtained by combining the on-state voltage-current (VI) characteristic of the power semiconductor device: Where V CE0 is the saturation voltage; R0 is the on-state resistance; I Cavg , I Crms are the average current and effective current flowing through the IGBT, I C is the capacitor current, T is a working cycle; Similarly, the conduction loss expressions of the fast recovery diode and thyristor in each phase bridge arm are: Where V FD0 、R FD0 are the saturation voltage and on-state resistance of the fast recovery diode respectively; I Davg , I Drms are the average value and effective value of the current flowing through the fast recovery diode respectively; V DW0 、R DW0 are the saturation voltage and on-state resistance of the thyristor respectively; I Wavg , I Wrms is the average value and effective value of the current flowing through the thyristor; The conduction loss of the power device in the previous stage circuit is obtained: P i1 =P S,con +P FD,con +P DW,con Step S4: The switching energy of the power device - current E sw The switching loss of the power device is calculated by fitting the I-I characteristic curve. This method reveals that the switching loss of the power device is proportional to the switching voltage and current. Specifically, the energy loss characteristic curve of the IGBT when it is turned on and off is combined to obtain the IGBT switching loss expression: Where, and They represent the average turn-on energy loss and average turn-off energy loss of IGBT, respectively. sw Indicates the switching frequency; Similarly, the reverse recovery loss of the fast recovery diode is: P D,rec =E D,rec f sw Where E D,rec represents the fast recovery diode voltage, f sw Indicates the switching frequency; The switching loss of the power device in the previous stage circuit is obtained: P i2 =P sw +P D,rec Step S5: Passive device loss is composed of inductance loss and capacitance loss. The Steinmetz equation is used in combination with the core loss curve of the amorphous alloy core to obtain the inductance loss expression: Where P core is the core loss, W Fe is the core weight, ρ cu Resistivity, l L Indicates length, A W Represents the cross-sectional area; I L,rms is the effective value of the inductor current, W is the unit of electrical energy work, kg is the unit of weight kilogram; Similarly, the calculation expression of filter capacitor loss can be obtained as follows: Where, I C,rms is the effective value of the current flowing through the capacitor, R C,ESR is the equivalent series resistance of the filter capacitor; The passive device loss of the front stage circuit is obtained: P i3 =P L +P C Step S6: Obtain the loss of the front-stage VIENNA rectification loss model from steps S3, S4, and S5: P i =P i1 +P i2 +P i3 。 2. A method for analyzing the loss of a charging pile circuit according to claim 1, characterized in that: The method further includes the following steps: Step S7: According to the LLC resonant characteristics of the compensation network, the MOS tube in the switch network is turned on at zero voltage, and only the conduction loss P needs to be calculated. ON and turn-off loss P S Since the current flowing through M1 to M4 is equivalent to a sine wave, assuming that LLC works at a resistive point, the effective value of the current flowing through a single switch tube can be obtained as I rms_s1 , we get the MOSFET conduction loss formula: P ON =(I rms_s1 ) 2 ×R DS Among them, R DS is the on-resistance; According to the turn-off transient process of the switch tube, the MOSFET turn-off loss formula is: Among them, V in_max is the maximum voltage when turned off, I off is the maximum current when shutting down, f s_max is the maximum operating frequency of the circuit, t p is the voltage rise time when turning off, t s is the current fall time when turning off; Step S8: Given the parameter values ​​of the resonant inductor, design the inductor according to the AP method and calculate the winding AC resistance R. act , the copper loss P of the resonant inductor can be obtained cu , iron loss P fe The coefficient K can be obtained by fitting the relationship curve between core loss and magnetic flux density based on the resonant frequency and the specific materials used. c , α, β, and finally calculate the loss of the resonant inductor in the compensation network, where V c is the core volume, the loss of the resonant capacitor can be ignored, and the specific formula for the resonant inductor loss is as follows: Step S9: Calculate the transformer winding loss in the rectifier filter network; calculate the primary and secondary winding AC resistance R according to the maximum power of the transformer. dctp 、R dcts , combined with the transformer current effective value i rm , we get the winding loss formula P w as follows: P w =P wp +P ws =(R dctp +R dcts )×i rm 2 Step S10: The calculation method of transformer core loss is the same as step S8, and the transformer loss is obtained as follows: Step S11, calculate the rectifier diode loss P CD : Among them, I F is the average forward current, V F is the forward voltage, T S For one working cycle; The loss of the subsequent DC / DC isolation loss model is obtained from steps S7-S11: P d =P ON +P S +P cw +P Tw +P CD Step S12: Introducing loss coefficient w i 、w j , according to the experimental data, the loss curve based on 25℃ is fitted to obtain w i and w j , we get the loss calculation prediction formula: P all =w i P i +w j P d Step S13: The operating efficiency of the corresponding charging pile is obtained by calculating the percentage of the loss amount to the actual power obtained according to the loss model. If the efficiency meets the specific design requirements, it can be determined that the performance of the charging pile is better. If the actual operating efficiency of the charging pile far exceeds the value calculated by the model, it can be determined that the charging pile is abnormal and a circuit fault has occurred.

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