Low-voltage power supply frequency converter for electric vehicles

Abstract

The application relates to a low-voltage power supply frequency converter for an electric vehicle, which comprises a ripple absorption circuit, a main power circuit, a control driving circuit and a discharge protection circuit; the ripple absorption circuit is connected on a direct-current bus between a direct-current power supply and the main power circuit, is used for ripple absorption of the direct-current power supply and direct-current energy storage of the bus; the control driving circuit is connected with the main power circuit, drives the main power circuit, and makes the main power circuit supply power to a motor; the discharge protection circuit is connected on the direct-current bus, is used for discharging the direct-current energy storage of the bus or motor feedback energy in a motor parking state, a braking state and a fault state. The application realizes frequency conversion and speed regulation of the motor; and realizes discharging the direct-current energy storage of the bus or the motor feedback energy in the motor parking state, the braking state and the fault state.

Description

Technical Field

[0001] This invention belongs to the field of electric vehicle technology, and specifically relates to a low-voltage power supply frequency converter for electric vehicles. Background Technology

[0002] With its mature and excellent speed regulation performance, the frequency converter is increasingly widely used in the speed regulation of electric vehicles.

[0003] When an electric vehicle is braking or stopping rapidly, the rotor speed of the motor will not suddenly drop to zero due to inertia. At this time, the motor is in a regenerative power generation state, which generates feedback current. This feedback current is fed back to the intermediate DC circuit through the anti-parallel diodes of the inverter bridge IGBT of the frequency converter. Although a capacitor is connected in parallel in the DC circuit of a general frequency converter, the capacitance of the capacitor is limited and cannot absorb all the feedback energy. Moreover, when the load inertia is particularly large or braking is frequent, the feedback energy is even greater. At this time, the built-in capacitor of the frequency converter is unable to store this part of the energy, causing the built-in capacitor to exceed its withstand voltage and be damaged, resulting in damage to the frequency converter.

[0004] Furthermore, when the motor is stationary at zero speed in an electric vehicle, or when there is a drive failure, the energy stored in the DC bus may cause false triggering or damage to the inverter.

[0005] Currently, the common approach of connecting the frequency converter to an external braking resistor or using a separate discharge branch for braking has two drawbacks. Firstly, it may not meet the requirements for rapid discharge. Secondly, it increases circuit complexity, control complexity, and reduces reliability by adding more discharge branches. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to disclose a low-voltage power supply frequency converter for electric vehicles, which realizes variable frequency speed regulation of electric vehicles and solves the problem of rapid discharge of DC energy storage on the bus or motor feedback energy.

[0007] This invention discloses a low-voltage power supply frequency converter for electric vehicles, comprising: a ripple absorption circuit, a main power circuit, a control drive circuit, and a discharge protection circuit;

[0008] The ripple absorption circuit is connected to the DC bus between the DC power supply and the main power circuit, and is used to absorb ripple of the DC power supply and store DC energy on the bus.

[0009] The control drive circuit is connected to the main power circuit and drives the main power circuit to supply power to the motor.

[0010] The discharge protection circuit is connected to the DC bus and is used to discharge the DC energy stored on the bus or the energy fed back by the motor in the motor stop state, braking state and fault state.

[0011] Furthermore, the discharge protection circuit includes a discharge resistor R. b 1. Discharge power circuit and discharge control circuit;

[0012] The discharge control circuit determines whether the motor is in a stopped state, a braking state, or a fault state based on the collected signals, and outputs a discharge drive signal to the discharge power circuit according to the state.

[0013] The power discharge device in the power discharge circuit is a switching transistor Q7; the drain of the switching transistor Q7 is connected to a discharge resistor R. b The source is connected to the positive power supply line of the DC bus, and the gate is connected to the negative power supply line of the DC bus; the gate is connected to the discharge control circuit through a drive resistor to output a discharge drive signal; when the discharge drive signal controls the switch Q7 to turn on, the switch Q7 and the discharge resistor R... b The discharge path forms a discharge path that discharges onto the DC bus.

[0014] Furthermore, the discharge protection circuit also includes a protection diode D1;

[0015] The protection diode D1 and the discharge resistor R b The circuit is connected in parallel, with the anode connected to the drain of the switching transistor Q7 and the cathode connected to the positive power supply line of the DC bus. When the switching transistor Q7 is turned on and the DC bus voltage is reversed, a path will be formed through the switching transistor Q7 and the diode D1, forming a closed loop with the power supply of the DC bus, causing a power short circuit, which will trigger the overcurrent protection of the power supply and stop supplying power to the frequency converter.

[0016] Furthermore, the discharge control process of the discharge control circuit includes:

[0017] 1) Determine if the motor is in a stopped state; if not, proceed to the next step; if yes, proceed to the first discharge process, discharge the bus voltage to zero and then stop the discharge.

[0018] 2) Determine if a drive signal fault has occurred; if not, proceed to the next step; then, through the first discharge process, discharge the bus voltage to zero and then stop the discharge;

[0019] 3) Determine if an overvoltage fault has occurred on the bus. If not, proceed to the next step; if yes, proceed to the second discharge process to discharge the bus voltage to the standard voltage value and then stop the discharge.

[0020] 4) Determine if an overcurrent fault has occurred in the bus current. If not, proceed to the next step. If yes, control the switching transistors Q1 to Q6 of the main power circuit of the frequency converter to turn off, and then discharge the bus voltage to the standard voltage value through the second discharge process before stopping the discharge.

[0021] 5) Determine if a bus voltage undervoltage fault has occurred. If not, proceed to the next step; if yes, output a control signal to turn off the switching transistor Q7.

[0022] 6) Determine whether the motor is in braking state based on whether the product of the collected motor angular velocity and angular acceleration is less than zero. If not, output a control signal to turn off the switch Q7. If yes, then through the third discharge process, discharge the bus voltage to the voltage standard value and then stop the discharge.

[0023] Furthermore, the first venting process includes:

[0024] The output control signal turns on the switching transistor Q7 of the power discharge circuit, and the power is discharged through the switching transistor Q7 and the discharge resistor R. b The discharge path forms a discharge path that discharges onto the DC bus;

[0025] During the discharge process, it is continuously determined whether the bus voltage is zero; if not, the switch Q7 is kept on; if yes, a control signal is output to turn off the switch Q7, and the discharge ends.

[0026] Furthermore, the second venting process includes:

[0027] The output control signal turns on the switching transistor Q7 of the power discharge circuit, and the power is discharged through the switching transistor Q7 and the discharge resistor R. b The discharge path forms a discharge path that discharges onto the DC bus;

[0028] During the discharge process, it is continuously determined whether the bus voltage drops to the standard value of the DC bus voltage; if not, the switch Q7 is kept on; if yes, a control signal is output to turn off the switch Q7, and the discharge ends.

[0029] Furthermore, the third venting process includes:

[0030] If the detected bus voltage reaches the upper threshold of the DC bus voltage, a control signal is output to turn on the switching transistor Q7 of the discharge power circuit. This signal is then transmitted through the switching transistor Q7 and the discharge resistor R. b The discharge path forms a discharge path that discharges onto the DC bus;

[0031] During the discharge process, continuously check whether the bus voltage drops to the standard value of DC bus voltage; if not, return to step 6); if yes, output a control signal to turn off the switch Q7 and the discharge ends.

[0032] Furthermore, the ripple absorption circuit includes a first absorption circuit and a second absorption circuit.

[0033] The first absorption circuit is used to absorb high-frequency ripple on the DC bus, including capacitors C41 and C42 connected in series between the positive and negative power supply lines of the DC bus, capacitors C43 and C44 connected in series, and resistors R41 and R42 connected in series; the connection terminals of capacitors C41 and C42 are connected together with the connection terminals of capacitors C43 and C44.

[0034] The second absorption circuit is used to absorb low-frequency ripple on the DC bus and perform DC energy storage on the bus; it includes capacitors ECC1-ECC4 connected in parallel between the positive and negative power supply lines of the DC bus as filtering and energy storage elements; and resistors R44-R48 connected in parallel between the positive and negative power supply lines of the DC bus.

[0035] Furthermore, based on both static and dynamic scenarios, the discharge resistor R is determined. b Resistance value and power rating;

[0036] In the static state, the motor powered by the low-voltage frequency converter does not rotate;

[0037] In the aforementioned dynamic scenario, the motor powered by the low-voltage frequency converter rotates and is in a braking state.

[0038] Furthermore, under static conditions, the determined discharge resistance R b Resistance value:

[0039]

[0040] Power rating:

[0041]

[0042] Under dynamic conditions, the determined bleed resistor R b Resistance value:

[0043]

[0044]

[0045]

[0046] Power rating:

[0047]

[0048]

[0049] In the formula, t r It is the safe discharge period, U safeIt is the safe DC bus voltage value, U dc0 The initial value of DC bus discharge is given by C'e, where C'e is the voltage constant and ψ is the initial value of the DC bus discharge. f It is a permanent magnet flux linkage, p is the number of pole pairs of the motor, i bRMS Q is the root mean square value of the discharge current. b It is the energy that needs to be dissipated, J is the moment of inertia of the motor, and R is the energy that needs to be dissipated. s It is the resistance value of the motor winding, ω m0 It is the initial value of angular velocity, ω. th It is the angular velocity value.

[0050] The present invention can achieve at least the following beneficial effects:

[0051] The low-voltage power supply inverter for electric vehicles of the present invention realizes variable frequency speed regulation of the motor; and enables the discharge of DC energy stored on the bus or the motor feedback energy in the motor stop state, braking state, and fault state. Specifically, in the motor stop state and in the drive control signal fault state, all DC energy stored on the bus is discharged quickly, avoiding electric shock problems caused by the DC bus being energized in the stop or maintenance state; in the overvoltage and overcurrent fault state, the energy caused by overcurrent and overvoltage is discharged, preventing damage to the circuit by overvoltage and overcurrent faults; in the braking state, it realizes both rapid discharge of motor feedback energy and prevents energy loss caused by the complete discharge of DC energy stored on the bus. Attached Figure Description

[0052] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0053] Figure 1 This is a block diagram illustrating the principle of a low-voltage power supply inverter for electric vehicles in an embodiment of the present invention.

[0054] Figure 2 This is a circuit diagram of the ripple absorption circuit in an embodiment of the present invention;

[0055] Figure 3 This is a schematic diagram of the main power circuit in an embodiment of the present invention;

[0056] Figure 4 This is a schematic diagram of the bus current acquisition and conditioning circuit in an embodiment of the present invention;

[0057] Figure 5 This is a schematic diagram of the control drive circuit in an embodiment of the present invention;

[0058] Figure 6 This is a block diagram of the discharge protection circuit in an embodiment of the present invention;

[0059] Figure 7This is a flowchart of the discharge control process of the discharge control circuit in an embodiment of the present invention. Detailed Implementation

[0060] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0061] One embodiment of the present invention discloses a low-voltage power supply frequency converter for electric vehicles, such as... Figure 1 As shown, it includes: a ripple absorption circuit, a main power circuit, a control drive circuit, and a discharge protection circuit;

[0062] The ripple absorption circuit is connected to the DC bus between the DC power supply and the main power circuit, and is used to absorb ripple of the DC power supply and store DC energy on the bus.

[0063] The control drive circuit is connected to the main power circuit and drives the main power circuit to supply power to the motor.

[0064] The discharge protection circuit is connected to the DC bus and is used to discharge the DC energy stored on the bus or the energy fed back by the motor in the motor stop state, braking state and fault state.

[0065] It also includes a data acquisition and conditioning circuit, which acquires the voltage and current signals of the DC bus and the current signal output by the main power circuit, and conditions the acquired signals to output the conditioned voltage and current signals.

[0066] Specifically, such as Figure 2 As shown, the ripple absorption circuit includes a first absorption circuit and a second absorption circuit.

[0067] The first absorption circuit is used to absorb high-frequency ripple on the DC bus, including capacitors C41 and C42 connected in series between the positive and negative power supply lines of the DC bus, capacitors C43 and C44 connected in series, and resistors R41 and R42 connected in series; the connection terminals of capacitors C41 and C42 are connected together with the connection terminals of capacitors C43 and C44.

[0068] The second absorption circuit is used to absorb low-frequency ripple on the DC bus and store DC energy on the bus; it includes capacitors ECC1-ECC4 connected in parallel between the positive and negative power supply lines of the DC bus as filtering and energy storage elements; and resistors R43-R46 connected in parallel between the positive and negative power supply lines of the DC bus.

[0069] In a preferred embodiment, a reverse connection protection circuit is further included between the first absorption circuit and the second absorption circuit. The reverse connection protection circuit includes resistors R47-R49, a Zener diode D12, and a switching transistor Q9.

[0070] The source and drain of the switching transistor Q9 are respectively connected to the negative terminal connection line of the DC bus in the first absorption circuit and the second absorption circuit; the gate is connected to the positive terminal connection line of the DC bus through resistor R49.

[0071] Zener diode D12 is connected between the gate and source of Q9, its cathode is connected to the gate of switching transistor Q9, its anode is connected to the negative terminal of the DC bus of the first absorption circuit, and is connected to the positive terminal of the DC bus through series resistors R47 and R48.

[0072] When the DC bus power supply is positively connected, the positively connected power supply turns on the switch Q9. The turned-on switch Q9 turns on the negative terminal connection line of the DC bus in the first absorption circuit and the second absorption circuit, thus turning on the negative terminal connection line of the DC bus. The power supply then supplies power to the subsequent circuits through the DC bus.

[0073] When the DC bus power supply is reversed, the positively connected power supply causes the switch Q9 to be cut off. The conducting switch Q9 disconnects the negative connection line of the DC bus in the first absorption circuit and the second absorption circuit, thus disconnecting the negative connection line of the DC bus. The reversed power supply cannot enter the subsequent circuit through the DC bus.

[0074] Specifically, such as Figure 3 As shown, the main power circuit includes a three-phase inverter bridge circuit, and "○" in the figure represents a current sensor.

[0075] The three-phase inverter bridge circuit uses the NPN type switch IRF3415 as the power conversion device.

[0076] The three-phase inverter bridge circuit is connected to the DC bus after ripple absorption and DC energy storage by the ripple absorption circuit.

[0077] The gate of each switch is connected to the control drive circuit through a drive resistor and is controlled by a drive signal; a Zener diode and a resistor are added in parallel between the gate and source terminals of the switch to stabilize the voltage between the gate and source terminals; a discharge branch consisting of a resistor and a reverse-connected diode is added in parallel with the drive resistor for reliable turn-off of the switch.

[0078] Specifically, taking a single bridge arm switch Q1 of a three-phase inverter bridge circuit as an example, the gate of switch Q1 is connected to the control drive circuit through a drive resistor R51 to receive the drive signal Q. 1-VControl; add a Zener diode D512 and a resistor R512 in parallel between the gate and source terminals of the switching transistor Q1 to stabilize the voltage between the gate and source terminals; add a discharge branch consisting of a resistor R511 and a reverse-connected diode D5112 in parallel with the drive resistor for reliable turn-off of the switching transistor. When the drive signal Q... 1-V When the voltage level is low, if the gate of switch Q1 is still high, D511 will conduct, thus connecting R511 and R51 in parallel. After parallel connection, Q... 1-V The resistance to the gate of the switch Q1 decreases significantly, and the gate of the switch Q1 discharges rapidly, dropping to a low level, thus achieving reliable turn-off of the switch Q1 and preventing false triggering of the switch Q1.

[0079] The three-phase inverter bridge circuit also includes a support capacitor C50 connected between the positive and negative terminals of the DC bus to absorb the ripple generated by the IGBT switching.

[0080] The acquisition and conditioning circuit includes a bus voltage acquisition circuit, a bus current acquisition circuit, and a three-phase current signal acquisition circuit;

[0081] The bus voltage acquisition circuit includes a bus voltage acquisition sensor and a bus voltage conditioning circuit;

[0082] The bus voltage acquisition sensor is located near the energy storage element on the DC bus and is used to acquire the DC bus voltage.

[0083] The bus voltage conditioning circuit is used to condition and output the acquired DC bus voltage signal. The DC bus voltage signal acquired by the bus voltage acquisition circuit can be used for overvoltage protection and to control the discharge circuit to discharge the DC bus.

[0084] Preferably, the bus voltage acquisition circuit uses a voltage acquisition sensor HV25-P to acquire the bus voltage.

[0085] The bus current acquisition and conditioning circuit includes a bus current acquisition sensor and a bus voltage conditioning circuit.

[0086] The bus current acquisition sensor is located near the positive terminal of the DC bus connected to the three-phase inverter bridge circuit.

[0087] The bus voltage conditioning circuit is used to condition the collected bus current and output an overcurrent output signal Itrip.

[0088] like Figure 4 As shown, the bus voltage conditioning circuit includes resistors R71-R75, operational amplifier U71, and optocoupler U72.

[0089] The operational amplifier U71 is powered by analog +5V. Its non-inverting input is connected to the output of the current acquisition sensor. The inverting input receives a reference voltage, which is generated by a series voltage divider circuit consisting of R71 and R72 connected in series between analog +5V and analog ground. The output is connected to analog +5V through pull-up resistor R73 and to the positive terminal of the light-emitting side of optocoupler U72 through resistor R74.

[0090] The positive terminal of the light-emitting side of optocoupler U72 is connected to the output terminal of operational amplifier U71 through resistor R74, and the negative terminal is connected to analog ground. The transmitter on the light-receiving side is connected to digital ground, and the collector is connected to digital +5V through pull-up resistor R75. The output signal is Itrip, which is an overcurrent output signal.

[0091] When the voltage value corresponding to the current acquisition value IDC output by the current acquisition sensor is greater than the reference voltage, the operational amplifier U71 outputs a high level, causing the light-emitting side of the optocoupler U72 to emit light, the light-receiving side to conduct, and the collector to conduct with the digital ground, causing the overcurrent output signal Itrip to go low, indicating an overcurrent.

[0092] The three-phase current signal acquisition circuit includes three current acquisition sensors and a three-phase current acquisition signal conditioning circuit.

[0093] The three current acquisition sensors are connected at the three-phase output terminals of the three-phase inverter bridge circuit.

[0094] The three-phase current acquisition signal conditioning circuit is used to amplify the acquired three-phase current for closed-loop control of the motor current loop.

[0095] Preferably, the current acquisition sensor is a non-contact current acquisition sensor LH25-NP; the output terminal of LH25-NP is connected to ground by an RC filter network, which is an RC parallel resonant network, wherein the resistor R is used in a resistor network to improve accuracy in order to meet the accuracy of current sampling.

[0096] like Figure 5 As shown, the control drive circuit includes a three-phase bridge drive chip U6; the Vcc pin of the three-phase bridge drive chip U6 is connected to a +15V power supply, the Vss pin is grounded to PGND, and a capacitor C51 is connected in parallel between +15V and PGND to absorb ripple noise.

[0097] The six control signals DRPWM1 to DRPWM6 to be driven are input from HIN1 to HIN6 respectively;

[0098] HO1,2,3 are connected to the gates of the three MOSFETs in the three upper arms of the three-phase bridge of the main power circuit, respectively; LO1,2,3 are connected to the gates of the MOSFETs in the three lower arms of the three-phase bridge, respectively.

[0099] Diode D62 is connected in series from the Vcc pin to VB, and a resistor R62 is connected in series to limit the current of the diode. Similarly, diode D53 is connected from Vcc to VB2, and a current-limiting resistor R63 is connected in series to protect diode D63. Diode D64 is connected from Vcc to VB3, and a resistor R64 is connected in series to protect diode D64. Ripple absorption capacitors C62, C63, and C64 are connected between VB and VS1, VB2 and VS2, and VB3 and VS3.

[0100] The Fault pin is used for detecting DC bus overcurrent and chip power supply undervoltage faults. When an overcurrent fault occurs in the DC bus current IDC, or the chip power supply Vcc is insufficient, the Fault pin outputs a low level. The Fault pin is connected to LED D61. The anode of LED D61 is connected to the +15V power supply through the current limiting resistor R61, and the cathode is connected to the Fault pin. When an overcurrent or undervoltage fault occurs, the Fault pin outputs a low level, the fault indicator lights up, and the outputs HO1,2,3 and LO1,2,3 of the drive circuit are turned off.

[0101] The Itrip pin is used to connect to the output of the bus current acquisition and conditioning circuit. When the Itrip pin is connected to a low level, the outputs HO1,2,3 and LO1,2,3 of the drive circuit are turned off.

[0102] When the DC bus current is overcurrent, the output terminal of the bus current acquisition and conditioning circuit outputs a low level to the Itrip pin, shutting down the outputs HO1,2,3 and LO1,2,3 of the drive circuit to stop driving the main power circuit, thereby achieving overcurrent protection.

[0103] The output signal of the Fault pin is also output after optocoupler isolation in order to realize the reporting of overcurrent faults.

[0104] like Figure 6 As shown, the discharge protection circuit includes a discharge resistor R. b Diode D1, power discharge circuit and power discharge control circuit;

[0105] The discharge control circuit determines whether the motor is in a stopped state, a braking state, or a fault state based on the collected signals, and outputs a discharge drive signal to the discharge power circuit according to the state.

[0106] The power discharge device in the power discharge circuit is a switching transistor Q7; the drain of the switching transistor Q7 is connected to a discharge resistor R. b The source is connected to the positive power supply line of the DC bus, and the gate is connected to the negative power supply line of the DC bus; the gate is connected to the discharge control circuit through a drive resistor to output a discharge drive signal; when the discharge drive signal controls the switch Q7 to turn on, the switch Q7 and the discharge resistor R...b The discharge path forms a discharge path that discharges onto the DC bus;

[0107] The protection diode D1 and the discharge resistor R b The circuit is connected in parallel, with the anode connected to the drain of switching transistor Q7 and the cathode connected to the positive power supply line of the DC bus. When switching transistor Q7 is turned on and a reverse voltage appears on the DC bus, the reverse voltage will be discharged through the path formed by switching transistor Q7 and diode D1. Since there are no power devices in the discharge circuit, the reverse voltage discharged through the path formed by switching transistor Q7 and diode D1 will generate a very strong discharge current, thus protecting the power devices of the main power circuit at the cost of damaging diode D1. In subsequent inspections, checking whether diode D1 is damaged helps determine if a reverse voltage occurred.

[0108] In the power discharge circuit, the gate of the switching transistor Q7 is connected to the discharge control circuit through a drive resistor and is controlled by the discharge drive signal; a Zener diode and a resistor are added in parallel between the gate and source terminals of the switching transistor Q7 to stabilize the voltage between the gate and source terminals; a discharge branch consisting of a resistor and a reverse-connected diode is added in parallel with the drive resistor for reliable turn-off of the switching transistor.

[0109] Specifically, such as Figure 7 As shown, the discharge control process of the discharge control circuit includes:

[0110] 1) Determine if the motor is in a stopped state; if not, proceed to the next step; if yes, proceed to the first discharge process, discharge the bus voltage to zero and then stop the discharge.

[0111] Specifically, when the detected motor angular velocity ω = 0, it is determined that the motor is in a stopped state;

[0112] 2) Determine if a drive signal fault has occurred; if not, proceed to the next step; then, through the first discharge process, discharge the bus voltage to zero and then stop the discharge.

[0113] When the acquired drive signal Q is detected 1-V ~Q 6-V When a driver error, including timing errors, occurs, check the driver signal Q. 1-V ~Q 6-V Fault;

[0114] 3) Determine if an overvoltage fault has occurred on the bus. If not, proceed to the next step; if yes, proceed to the second discharge process to discharge the bus voltage to the standard voltage value and then stop the discharge.

[0115] When the collected bus voltage U is detected dc Exceeding the upper threshold voltage U of the DC bus dcuslWhen this occurs, an overvoltage fault is detected;

[0116] DC bus voltage upper threshold U dcusl It is determined by the withstand voltage of the main power circuit switching transistor and the reverse breakdown voltage of the anti-parallel diode.

[0117] 4) Determine if an overcurrent fault has occurred in the bus current. If not, proceed to the next step. If yes, control the switching transistors Q1 to Q6 of the main power circuit of the frequency converter to turn off, and then discharge the bus voltage to the standard voltage value through the second discharge process before stopping the discharge.

[0118] When the collected bus current I is detected dc Exceeding the DC bus current threshold value I dcth When an overcurrent fault occurs, it is determined that an overcurrent fault has occurred.

[0119] DC bus current threshold I dcth The current is determined by the leakage current of the main power circuit switching transistor and the current that the anti-parallel diode can withstand.

[0120] 5) Determine if a bus voltage undervoltage fault has occurred. If not, proceed to the next step; if yes, output a control signal to turn off the switching transistor Q7.

[0121] When the collected bus voltage U is detected dc Below the threshold U of DC bus voltage dclsl When this occurs, an undervoltage fault is detected;

[0122] DC bus voltage threshold U dclsl The system stability is determined by the power supply voltage and the frequency converter.

[0123] 6) Determine whether the motor is in braking state based on whether the product of the collected motor angular velocity and angular acceleration is less than zero. If not, output a control signal to turn off the switch Q7. If yes, then through the third discharge process, discharge the bus voltage to the standard voltage value and then stop the discharge.

[0124] The above discharge control process is repeated to continuously provide discharge protection for the frequency converter.

[0125] Specifically, the first discharge process includes:

[0126] The output control signal turns on the switching transistor Q7 of the power discharge circuit, and the power is discharged through the switching transistor Q7 and the discharge resistor R. b The discharge path forms a discharge path that discharges onto the DC bus;

[0127] During the discharge process, it is continuously determined whether the bus voltage is zero; if not, the switch Q7 is kept on; if yes, a control signal is output to turn off the switch Q7, and the discharge ends.

[0128] Specifically, the second venting process includes:

[0129] The output control signal turns on the switching transistor Q7 of the power discharge circuit, and the power is discharged through the switching transistor Q7 and the discharge resistor R. b The discharge path forms a discharge path that discharges onto the DC bus;

[0130] During the discharge process, it is continuously determined whether the bus voltage drops to the standard value U of the DC bus voltage. dcstd If no, then keep switch Q7 on; if yes, then output a control signal to turn off switch Q7, and the discharge ends.

[0131] The third discharge process includes:

[0132] The bus voltage U collected by the detection dc Has the DC bus voltage threshold U been reached? dcusl If yes, then the output control signal turns on the switching transistor Q7 of the power discharge circuit, and through the switching transistor Q7 and the discharge resistor R... b The discharge path forms a discharge path that discharges onto the DC bus;

[0133] During the discharge process, the bus voltage U is continuously monitored. dc If the voltage is reduced to the standard value of the DC bus voltage, then return to step 6; if yes, then output a control signal to turn off the switching transistor Q7 and stop the discharge.

[0134] In the discharge protection circuit, the discharge resistor R b As the main energy-consuming device for bleeding, its resistance and power rating need to meet the power requirements of bleeding.

[0135] Specifically, in this embodiment, the discharge resistor R is determined based on two scenarios: a static scenario and a dynamic scenario. b Resistance value and power rating.

[0136] In a static case,

[0137] The motor speed is zero, and active discharge occurs; no residual energy is stored in the motor, only the DC bus capacitor voltage needs to be reduced. Therefore, the PMSM and inverter are in a non-operating state, while the capacitor and bleeder circuit are operational. In this case, the capacitor and bleeder form a simple resistive-capacitive network, so the real-time capacitor voltage Udc during discharge is expressed as...

[0138]

[0139] Where Udc0 is the initial bus voltage, equal to the output of the DC-DC boost converter. C is the capacitance of the bus. Assuming the required discharge cycle and the safe DC bus voltage are denoted as tr and Usafe respectively, the required bleed resistor Rb can be derived as follows:

[0140]

[0141] When designing a winding braking resistor, besides resistance, current-carrying capacity is another key parameter determining the wire size (diameter and length). During discharge, the total energy Qb that needs to be dissipated is...

[0142]

[0143] Therefore, the root mean square (rms) discharge current i bRMS for

[0144]

[0145] In dynamic situations,

[0146] In the event of an emergency while the vehicle is traveling on the road, the kinetic energy of the PMSM rotor and the energy stored in the bus capacitors should be consumed by the discharge resistor.

[0147] During energy consumption, the motor operates in generator mode, causing the back EMF, which is related to the motor speed, to continuously decrease. For the inverter, the inherent protection mode is triggered in an emergency, and a "shutdown" control signal is applied to all transistors. The six freewheeling diodes cannot be in the off state, forming an uncontrolled rectifier (UR). The motor's back EMF is rectified by the uncontrolled rectifier UR, charging the capacitor and generating a discharge current i through the discharge resistor BR. b .

[0148] To reduce the complexity of the analysis, it can be appropriately assumed that the effect of the motor winding inductance is negligible, as it is very small. Based on this, the braking q-axis current i in the motor... q The magnitude is equal to the discharge current i b (Active current), the d-axis current is 0, that is...

[0149]

[0150] Furthermore, the bus capacitor voltage can be approximated as

[0151]

[0152] Where C e ' is the voltage constant. Ψ f It is the magnetic flux of the permanent magnet. ω m It is angular velocity. The electromagnetic torque T of a surface-mount permanent magnet synchronous motor (SPMSM) e The following description is provided:

[0153] T e =1.5pψ f iq ≈-1.5pψ f i b (7)

[0154] The actual motor speed can be expressed as:

[0155]

[0156] Where ω m0 It is the initial rotational speed. J is the moment of inertia. Substituting (5), (7), and (8) into (6), U dc It can be written as

[0157]

[0158] Taking the derivative of (9), the voltage drop rate (VDR) can be expressed as:

[0159]

[0160] Due to U dc Following a downward trend, according to (10), the voltage drop rate VDR will also continue to decrease. Therefore, at t r From this, we can deduce

[0161]

[0162] Based on (11), the BR discharge resistor should meet the following standards.

[0163]

[0164] in,

[0165]

[0166] Compared to zero speed, the energy consumed includes not only the electrical components stored in the capacitors, but also the kinetic energy in the motor rotor.

[0167]

[0168] Therefore, the root mean square discharge current is:

[0169]

[0170] Bleeding resistor R b Size and weight assessment

[0171] In this embodiment, the bleeder resistor R b A precision bleeder resistor is produced using a copper (Cu) and nickel (Ni) alloy as raw materials, with CuNi44 (ISOTAN@) selected as the resistor with a resistivity of ρ. r =49×10- 8Ω; and density ρ m =8900 kg / m3;

[0172] Calculations show that the conductor diameter d is related to the current carrying capacity i. ca The relationship yields the minimum wire diameter:

[0173] i ca =0.3516d 2 +2.6475d-0.1552. (15)

[0174] In a preferred embodiment, the discharge resistor R is used when the required discharge time is 5 seconds. b Performance:

[0175] R b The resistance is 7.33Ω, and the diameter d of the conductor is... b It is 4.5mm in diameter and has a length of l. b It measures 237.8m and weighs approximately 33.6kg.

[0176] In summary, the low-voltage power supply inverter for electric vehicles in this embodiment of the invention achieves variable frequency speed control of the motor; and it also enables the discharge of DC energy stored on the bus or the motor's regenerative energy in the motor's stopped, braking, and fault states. Specifically, in the motor stopped state and in the drive control signal fault state, all DC energy stored on the bus is quickly discharged, avoiding electric shock problems caused by the DC bus being energized during parking or maintenance; in the overvoltage and overcurrent fault state, the energy caused by overvoltage and overcurrent is discharged, preventing damage to the circuit due to overvoltage and overcurrent faults; in the braking state, it achieves both rapid discharge of motor regenerative energy and prevents energy loss caused by the complete discharge of DC energy stored on the bus.

[0177] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-voltage power supply frequency converter for electric vehicles, characterized in that, include: Ripple absorption circuit, main power circuit, control drive circuit and discharge protection circuit; The ripple absorption circuit is connected to the DC bus between the DC power supply and the main power circuit, and is used to absorb ripple of the DC power supply and store DC energy on the bus. The control drive circuit is connected to the main power circuit and drives the main power circuit to supply power to the motor. The discharge protection circuit is connected to the DC bus and is used to discharge the DC energy stored on the bus or the energy fed back by the motor in the motor stop state, braking state and fault state. The discharge protection circuit includes a discharge resistor R. b 1. Discharge power circuit and discharge control circuit; The discharge control circuit determines whether the motor is in a stopped state, a braking state, or a fault state based on the collected signals, and outputs a discharge drive signal to the discharge power circuit according to the state. The power discharge device in the power discharge circuit is a switching transistor Q7; the drain of the switching transistor Q7 is connected to a discharge resistor R. b The source is connected to the positive power supply line of the DC bus, and the gate is connected to the negative power supply line of the DC bus; the gate is connected to the discharge control circuit through a drive resistor to output a discharge drive signal; when the discharge drive signal controls the switch Q7 to turn on, the switch Q7 and the discharge resistor R... b The discharge path forms a discharge path that discharges onto the DC bus; The discharge control process of the discharge control circuit includes: 1) Determine if the motor is in a stopped state; if not, proceed to the next step; if yes, proceed to the first discharge process, discharge the bus voltage to zero and then stop the discharge. The first discharge process includes: The output control signal turns on the switching transistor Q7 of the power discharge circuit, and the power is discharged through the switching transistor Q7 and the discharge resistor R. b The discharge path forms a discharge path that discharges onto the DC bus; During the discharge process, it is continuously determined whether the bus voltage is zero; if not, the switch Q7 is kept on; if yes, a control signal is output to turn off the switch Q7, and the discharge ends. 2) Determine if a drive signal fault has occurred; if not, proceed to the next step; if yes, proceed through the first discharge process to discharge the bus voltage to zero and then stop the discharge. 3) Determine if an overvoltage fault has occurred on the bus voltage; if not, proceed to the next step; if yes, proceed to the second discharge process to discharge the bus voltage to the standard voltage value and then stop the discharge. The second discharge process includes: The output control signal turns on the switching transistor Q7 of the power discharge circuit, and the power is discharged through the switching transistor Q7 and the discharge resistor R. b The discharge path forms a discharge path that discharges onto the DC bus; During the discharge process, it is continuously determined whether the bus voltage drops to the standard value of the DC bus voltage; if not, the switch Q7 is kept on; if yes, a control signal is output to turn off the switch Q7, and the discharge ends. 4) Determine if an overcurrent fault has occurred in the bus current; if not, proceed to the next step; if yes, after the switching transistors Q1~Q6 of the main power circuit of the frequency converter are turned off, the bus voltage is discharged to the standard voltage value through the second discharge process and then the discharge stops. 5) Determine if an undervoltage fault has occurred on the bus; if not, proceed to the next step; if yes, output a control signal to turn off the switching transistor Q7. 6) Determine whether the motor is in braking state based on whether the product of the collected motor angular velocity and angular acceleration is less than zero; if not, output a control signal to turn off the switch Q7; if yes, then discharge the bus voltage to the standard voltage value through the third discharge process and then stop the discharge. The third discharge process includes: The system detects whether the collected bus voltage reaches the upper threshold of the DC bus voltage; if so, it outputs a control signal to turn on the switch Q7 of the discharge power circuit, and the power is released through the switch Q7 and the discharge resistor R. b The discharge path forms a discharge path that discharges onto the DC bus; During the discharge process, continuously check whether the bus voltage drops to the standard value of the DC bus voltage; if not, return to step 6); if yes, output a control signal to turn off the switch Q7, and the discharge ends.

2. The low-voltage power supply frequency converter for electric vehicles according to claim 1, characterized in that, The discharge protection circuit also includes a protection diode D1; The protection diode D1 and the discharge resistor R b The circuit is connected in parallel, with the anode connected to the drain of the switching transistor Q7 and the cathode connected to the positive power supply line of the DC bus. When the switching transistor Q7 is turned on and the DC bus voltage is reversed, a path will be formed through the switching transistor Q7 and the diode D1, forming a closed loop with the power supply of the DC bus, causing a power short circuit, which will trigger the overcurrent protection of the power supply and stop supplying power to the frequency converter.

3. The low-voltage power supply frequency converter for electric vehicles according to claim 1, characterized in that, The ripple absorption circuit includes a first absorption circuit and a second absorption circuit. The first absorption circuit is used to absorb high-frequency ripple on the DC bus, including capacitors C41 and C42 connected in series between the positive and negative power supply lines of the DC bus, capacitors C43 and C44 connected in series, and resistors R41 and R42 connected in series; the connection terminals of capacitors C41 and C42 are connected together with the connection terminals of capacitors C43 and C44. The second absorption circuit is used to absorb low-frequency ripple on the DC bus and perform DC energy storage on the bus; it includes capacitors ECC1-ECC4 connected in parallel between the positive and negative power supply lines of the DC bus as filtering and energy storage elements; and resistors R44-R48 connected in parallel between the positive and negative power supply lines of the DC bus.

4. The low-voltage power supply frequency converter for electric vehicles according to claim 1, characterized in that, Determine the bleeder resistor R based on both static and dynamic scenarios. b Resistance value and power rating; In the static state, the motor powered by the low-voltage frequency converter does not rotate; In the aforementioned dynamic scenario, the motor powered by the low-voltage frequency converter rotates and is in a braking state.

5. The low-voltage power supply frequency converter for electric vehicles according to claim 2, characterized in that, Under static conditions, the determined bleed resistance R b Resistance value: ； Power rating: ； Under dynamic conditions, the determined bleed resistor R b Resistance value: ； ； ； Power rating: ； ； In the formula, C It is the capacitance value of the busbar. t r It is the safe discharge period. U safe This is the safe DC bus voltage value. U dc0 This is the initial value for DC bus discharge. C'e It is the voltage constant. ψ f It is a permanent magnet flux chain. p It is the number of pole pairs of the motor. i bRMS This is the root mean square value of the discharge current. Q b It is the amount of energy that needs to be dissipated. J It is the moment of inertia of the motor. R s It is the resistance value of the motor winding. ω m0 It is the initial value of angular velocity. ω th That is the angular velocity value.

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