TWI699061B - A short circuit protection device with dc bus current detection method - Google Patents

Abstract

A method and device with bus current detection and short-circuit protection includes: a current detection circuit for detecting the voltage difference generated by three-phase current; a switch circuit connected between the current detection circuit and the ground terminal; and a signal processing The circuit is used to filter the high-frequency AC signal component current of the voltage difference, leaving the low-frequency signal component current, which is equivalent to the bus current; among them, the low-frequency signal component current of the voltage difference is filtered out, leaving the high-frequency AC signal component current, After integration, the first integrated current and the current rate of change are generated. If the first integrated current reaches the first critical value and the current rate of change reaches the second critical value, it is determined that a short circuit has occurred, and the switching circuit is started to cut off the three-phase current loop to reach It not only detects the bus current but also achieves the purpose of short circuit protection.

Description

Method and device with bus current detection and short circuit protection

The present invention relates to a method and device with bus current detection and short circuit protection, and more particularly to a power conversion circuit used in electric vehicle motors, which has a method for detecting bus current on the power supply side and instant micro short circuit protection And its devices.

According to the motor controller application of electric vehicles, it is generally necessary to detect the bus current on the power supply side for battery protection, power estimation, or motor output power curve control. Generally, the motor power conversion circuit detects the bus current on the power side, and cannot respond to the momentary short-circuit phenomenon immediately.

For example, China Patent Application No. 105205618 "IGBT short-circuit detection and protection circuit and IGBT-based controllable rectification circuit" can pass through the collector terminal of the diode and edge gate bipolar transistor (IGBT), and the voltage at the detection pin is greater than A threshold voltage is indicated as a short circuit.

Another example is China's Patent Application No. 103108665 "Bridge circuit with short circuit protection and its method", using the micro-optocoupler of the detection unit, when the detection unit detects that the capacitance current is greater than the preset current, the judgment is Short circuit.

As shown in Figure 1, it is a short-circuit protection circuit of a conventional three-phase motor control circuit. It can detect the currents T1~T3 flowing through the upper arm K1~K3 or lower arm K4~K6 of each three-phase switch. To achieve the purpose of short circuit detection. However, the above patented technology can only be used for short circuit protection or phase current Measurement, it is impossible to achieve short-circuit protection and the purpose of measuring the bus current on the power side.

As shown in Figure 2, if the conventional motor control circuit is to achieve phase current detection, it can be achieved in three ways. The first method is line current measurement. The line current measurement can be achieved by three Hall sensors (Hall S1~S3). Sensor) is added to the output terminal of the three-phase switch for measurement, which is called non-contact measurement. The second method is contact measurement, using three shunt resistors R1~R3 to be added to the upper or lower arm of the three-phase switch to measure. The third method is bus current measurement. For example, the reference "Single-Shunt Three-Phase Current Reconstruction Algorithm for Sensorless FOC of a PMSM" proposes a single shunt resistor R4 added to the ground terminal of the power supply side to achieve bus current measurement and phase current Detection, but the third method must be matched with the pulse width modulation (PWM) circuit sampling sequence to complete. If short-circuit protection is to be implemented, the reaction time will be too long and the short-circuit protection cannot be effectively achieved.

In order to solve the lack of conventional bus bar current detection and short circuit protection, the purpose of the present invention is to provide a method and device that can detect bus bar current and provide instant short circuit protection.

To achieve the above objective, the main technical feature of the present invention is to provide a method with bus current detection and short-circuit protection. Firstly, a three-phase current is detected to generate a voltage difference, and then the high frequency AC signal component current of the voltage difference is filtered out. , Leaving the low-frequency signal component current, which is equivalent to the bus current; at the same time, filter out the low-frequency signal component current of the voltage difference, leaving the high-frequency AC signal component current, and then integrate the high-frequency AC signal component current to generate the first integrated current and the first integrated current Two integrated currents, and then subtract the first integrated current and the second integrated current to generate a current rate of change, and finally compare whether the first integrated current reaches the first critical value, and compare whether the current rate of change reaches the second critical value If both of them are satisfied at the same time, it is judged as a short-circuit phenomenon, and the three-phase current loop is cut off to achieve the purpose of detecting bus current and short-circuit protection.

In order to achieve the above objective, the secondary technical feature of the present invention is to provide a device with bus current detection and short-circuit protection, including: a current detection circuit for detecting three-phase currents to generate a voltage difference; a switch circuit connected to the current detection Between the circuit and the ground terminal; and a signal processing circuit to filter out the high-frequency AC signal component current of the voltage difference, leaving the low-frequency signal component current, which is equivalent to the bus current; among them, the low-frequency signal component current of the voltage difference is filtered out ，Leave the high-frequency AC signal component current, and generate the first integrated current and the current rate of change after integration. If the first integrated current reaches the first critical value and the current rate of change reaches the second critical value at the same time, it is judged that a short-circuit phenomenon has occurred and start The switching circuit cuts off the loop of the three-phase current to achieve the purpose of detecting bus current and short-circuit protection.

To achieve the above object, the secondary technical feature of the present invention is to provide the above-mentioned device with bus current detection and short-circuit protection, wherein the signal processing circuit further includes: a low-pass filter for filtering out the high-frequency AC signal component current of the voltage difference , Leaving the low-frequency signal component current.

In order to achieve the above objective, the secondary technical feature of the present invention is to provide the above-mentioned device with bus current detection and short circuit protection, wherein the signal processing circuit further includes: a high-pass filter for filtering out the low-frequency signal component current of the voltage difference, leaving High frequency AC signal component current; a first integrator is used to integrate high frequency AC signal component current to generate a first integrated current; a second integrator is used to integrate high frequency AC signal component current to generate a second integrated current; a subtractor is used to The first integrated current is subtracted from the second integrated current to generate a current rate of change; a first comparator is used to compare whether the first integrated current reaches the first critical value; a second comparator is used to compare whether the current rate of change reaches the second critical value; A gate is used to determine when the first integral current reaches the first critical value, and at the same time When the current change rate reaches the second critical value, the output start switch circuit cuts off the three-phase current loop.

10: Three-phase power conversion circuit

11: Current detection circuit

12: Switch circuit

20: signal processing circuit

21: low pass filter

22: high pass filter

23: first integrator

24: second integrator

25: subtractor

251: One of the input terminals of the subtractor

252: The other input of the subtractor

253: The output of the subtractor

26: The first comparator

261: One of the input terminals of the first comparator

Q1~Q6: Power switch

Iu, Iv, Iw: the current of the three-phase power arm

Im: three-phase current

GND: ground terminal

Idc: ground current

Ic: capacitor current

Δv : voltage difference

I(t) : first integral current

I(t + Δt) : second integral current

x(t) : current rate of change

V_th1 : the first critical value

V_th2 : second critical value

Δx : current change

A, B: signal

262: The other input of the first comparator

263: The output of the first comparator

27: second comparator

271: One of the input terminals of the second comparator

272: The other input of the second comparator

273: The output of the second comparator

28: and gate

281: and gate output

Figure 1 is a short-circuit protection circuit of a conventional three-phase motor control circuit.

Figure 2 shows the conventional measurement methods of three currents: line current, phase current and bus current.

Figure 3 is a block diagram of the circuit of the present invention.

Figure 4 is a block diagram of the signal processing circuit of the present invention.

Fig. 5 is a schematic diagram of the waveform state when the short-circuit protection is activated according to the present invention.

Fig. 6 is a schematic diagram of the waveform state when the short circuit protection is not activated according to the present invention.

Please refer to FIG. 3 and FIG. 4 together. FIG. 3 is a block diagram of the circuit of the present invention, and FIG. 4 is a block diagram of the signal processing circuit of the present invention. The present invention is mainly used in a three-phase power conversion circuit 10 for electric vehicles from DC to AC. The three-phase power conversion circuit 10 is composed of six power switches Q1~Q6 to form a three-phase power arm, and every two power switches form a phase Power arm.

The short-circuit protection device of the present invention includes a current detection circuit 11, a switch circuit 12, and a signal processing circuit 20. The current detection circuit 11 connected to the three-phase power arm can be formed by a shunt resistor or a current sensing element for detecting a three-phase current Im. As shown in Figure 3, the three-phase current Im flowing through the current detection circuit 11 is composed of the currents Iu, Iv, Iw flowing through the three-phase power arm, that is, the three-phase current Im=f(Iu, Iv, Iw ).

The three-phase current Im is divided into the current Ic flowing through a capacitor and the current Idc flowing back to the ground terminal GND. Since the current Ic flowing through the capacitor must be an alternating high frequency current, and the current Idc flowing back to the ground terminal GND must be low frequency Current, so the low-frequency component current of the three-phase current Im is equivalent When the current Idc flows back to the ground terminal GND, in other words, the low-frequency component of the three-phase current Im is equivalent to the bus current of the three-phase power conversion circuit 10, and the high-frequency component current of the three-phase current Im is equivalent to the current flowing through Capacitor current Ic.

Please refer to FIG. 3 and FIG. 4 together. FIG. 4 is a block diagram of the signal processing circuit of the present invention. The switch circuit 12 may be composed of a field effect transistor (Mosfet), a relay (Relay) or other power components. The signal processing circuit 20 can distinguish the three-phase current Im into the low-frequency component current and the high-frequency component current to obtain the ground current Idc and the capacitor current Ic, and determine whether a short circuit occurs, and if so, the switching circuit will cut off The three-phase current Im flows to the loop of the ground terminal GND to achieve the purpose of protection.

As shown in FIG. 4, the signal processing circuit 20 includes a low-pass filter 21, a high-pass filter 22, a first integrator 23, a second integrator 24, a subtractor 25, and a first comparator 26. , A second comparator 27 and a gate 28, wherein the low-pass filter 21 and the high-pass filter 22 are connected to the current detection circuit 11, the three-phase current Im is detected by the current detection circuit 11 Then, a voltage difference Δv is generated, and the voltage difference Δv is divided into two paths. One way is filtered through the low-pass filter 21 to remove the high-frequency AC signal component current, leaving a low-frequency signal component current. The low-frequency signal component current is equivalent to the current The current Idc returning to the ground terminal GND, in other words, the bus current is the low-frequency signal component current Idc of the voltage difference Δv.

The other path of the voltage difference Δv filters the low-frequency signal component current through the high-pass filter 22, leaving a high-frequency AC signal component current. The magnitude of the high-frequency AC signal component current is proportional to the current phase current. The occurrence of short-circuit phenomenon can generally be studied and judged from two situations: (1) the magnitude of the high-frequency signal component current exceeds the expected maximum value; (2) the current change of the high-frequency signal component current exceeds the expected value in a short time, For example: (current change dI)/(time change Quantity dt)> X A/us, X=several amperes/microsecond.

If the utilization situation (1) the magnitude of the high-frequency signal component current exceeds the expected maximum value for short-circuit judgment, there will be a problem that the response time is not fast enough, but if the utilization situation (2) the current change amount of the high-frequency signal component current When the short circuit is judged by exceeding the expected value, the occurrence of the short circuit can be detected quickly. Assuming that the voltage difference Δv flowing through the current detection circuit 11, the current waveform is i(t), which can be expressed by the following formula after integration:

By (1) the current rate of change x(t) can be expressed as:

In the signal processing circuit 20 in FIG. 4, the first integrator 23 and the second integrator 24 are both connected to the high-pass filter 22, and the integration time constant of the second integrator 24 is longer than that of the first integrator 23 is one time change Δt. Therefore, the high-frequency signal component current of the voltage difference Δv is integrated by the first integrator 23 to generate a first integrated current I(t), which is then connected to an input terminal 261 of the first comparator 26, and is connected to the One input terminal 251 of the subtractor 25. The current signal of the high-frequency signal component of the voltage difference Δv is integrated by the second integrator 24 to generate a second integrated current I(t+Δt), and then connected to the other input terminal 252 of the subtractor 25. The subtractor 25 subtracts the second integrated current I(t+Δt) from the first integrator current I(t) to generate a current change rate x(t). The output terminal 253 of the subtractor 25 is connected to An input 271 of the second comparator 27.

The other input terminal 262 of the first comparator 26 can input a first threshold value V_th1. The first threshold value V_th1 represents the absolute value of the set expected current, and the expected current can be the current value to be protected by the system. The other input 272 of the second comparator 27 can input a second temporary The boundary value V_th2, the second critical value V_th2 represents the current change rate x(t) within the time change Δt, as described in equation (3), when the current change rate x(t) becomes larger, the time changes The measured current change Δx within the amount Δt is also larger.

When comparing whether the first integral current I(t) reaches the first critical value V_th1, and compare whether the current change rate x(t) reaches the second critical value V_th2, if both are met at the same time, it is judged that a short circuit phenomenon has occurred The output terminal 263 of the first comparator 26 and the output terminal 273 of the second comparator 27 are respectively output to the two input terminals of the AND gate 28, and the output terminal 281 of the AND gate 28 outputs a high potential to the switch circuit 12. , To cut off the loop of the three-phase current Im flowing to the ground terminal GND to achieve the purpose of short-circuit protection.

Please refer to FIGS. 3 and 5 together. FIG. 5 is a schematic diagram of the waveform state when the short-circuit protection is activated according to the present invention. The present invention assumes that when the time is 0 us, after a pulse signal of the three-phase current Im flows through the current detection circuit 11, a voltage difference Δv is generated, and the rise time is 0.8 us. It is shown in Fig. 5 that the signal B changes to a high potential at 1us, and the signal A also changes to a high potential at 1.2us. At this time, when the signals A and B are both at high potentials, the switch circuit 12 is triggered to cut off the switch. Start short circuit protection.

Please refer to Figures 3 and 6 together. Figure 6 is a schematic diagram of the waveform state of the present invention when the short-circuit protection is not activated. Assuming that a pulse signal of the three-phase current Im flows through the current detection circuit 11, a pulse signal is generated. The voltage difference Δv has a rise time of 8us. It is shown in Fig. 6 that the signal A changes to a high potential at 3.6us, but the signal B remains at a low potential. When the signals A and B cannot be high at the same time, the switch circuit 12 cannot be triggered, that is, the short circuit protection is not activated.

Since the load of the three-phase power conversion circuit 10 of the present invention is a motor under normal working conditions, which is an inductive load, the current change rate is related to the inductance, but it is much smaller than the current change rate during a short circuit. Therefore, it can be seen from Figure 6 that when the current change rate is small, although The absolute value of the three-phase current Im has reached the first critical value V_th1, but after being integrated by the second integrator, the relative difference with the second critical value V_th2 is very small, so the short circuit protection will not be triggered. It can be seen from Fig. 5 that when the current rate of change is large, the relative difference between the second integrator and the second critical value V_th2 is large, so the short-circuit protection is triggered at 1.2 us, and the response time is short. From the above analysis, it can be seen that the short circuit protection response time of the present invention can effectively shorten the judgment time than the method of judging short circuit by simply using the current magnitude, and can avoid misoperation under normal operation conditions and increase system reliability.

10: Three-phase power conversion circuit

11: Current detection circuit

12: Switch circuit

20: signal processing circuit

Q1~Q6: Power switch

Iu, Iv, Iw: the current of the three-phase power arm

Im: three-phase current

GND: ground terminal

Idc: ground current

Ic: capacitor current

Δv : voltage difference

Claims (21)

A method with bus current detection and short-circuit protection is used in a three-phase power conversion circuit from DC to AC. The method includes: Detect a three-phase current and generate a voltage difference; Filter out the high-frequency AC signal component current of the voltage difference, leaving a low-frequency signal component current, which is equivalent to the bus current; Filter out the low-frequency signal component current of the voltage difference, leaving a high-frequency AC signal component current; Integrating the component current of the high-frequency AC signal to generate a first integrated current and a second integrated current; The first integrated current is subtracted from the second integrated current to generate a current rate of change; and Compare whether the first integral current reaches a first critical value, and compare whether the current rate of change reaches a second critical value, if both are met at the same time, it is determined that a short circuit phenomenon has occurred, and the three-phase current loop is cut off. To achieve the purpose of detecting bus current and short-circuit protection. The method with bus current detection and short-circuit protection according to claim 1, wherein the three-phase current is composed of current flowing through a three-phase power arm. The method with bus current detection and short-circuit protection according to claim 2, wherein the three-phase power arm is composed of six power switches, and every two power switches form a power arm of one phase. The method with bus current detection and short-circuit protection according to claim 1, wherein the low-frequency component current of the three-phase current is equivalent to the current flowing back to a ground terminal. The method with bus current detection and short-circuit protection according to claim 1, wherein a low-pass filter is used to filter out the high-frequency AC signal component current of the voltage difference. The method with bus current detection and short circuit protection as described in claim 1, wherein the voltage is filtered out A high-pass filter is used for the poor low-frequency signal component current. The method with bus current detection and short-circuit protection according to claim 1, wherein integrating the high-frequency AC signal component current uses a first integrator to generate the first integrated current, and a second integrator to generate the The second integral current, wherein the integral time constant of the second integrator is larger than the first integrator by a time change amount. The method with bus current detection and short-circuit protection according to claim 1, wherein the first integrated current and the second integrated current are subtracted by using a subtractor. The method with bus current detection and short-circuit protection according to claim 1, wherein a first comparator is used to compare whether the first integrated current reaches the first critical value, and it is compared whether the current change rate reaches the first The second threshold is to use a second comparator. The method with bus current detection and short-circuit protection according to claim 1, wherein the first threshold value represents the absolute value of the set expected current. The method with bus current detection and short-circuit protection according to claim 1, wherein the second threshold value represents the current change rate within a time change. The method with bus current detection and short-circuit protection as described in claim 1, wherein a switching circuit is used to cut off the three-phase current loop. A device with bus current detection and short-circuit protection is used in a three-phase power conversion circuit from DC to AC. The device includes: A current detection circuit connected to a three-phase power arm to detect a three-phase current and generate a voltage difference; A switch circuit connected between the current detection circuit and a ground terminal; and A signal processing circuit connected to the current detection circuit and the switch circuit to filter out the The high-frequency AC signal component current of the voltage difference leaves a low-frequency signal component current, which is equivalent to a bus current; the low-frequency signal component current of the voltage difference is filtered out, leaving a high-frequency AC signal component current, which is integrated Then, a first integrated current and a current change rate are generated. If the first integrated current reaches a first critical value and at the same time the current change rate reaches a second critical value, it is determined that a short-circuit phenomenon has occurred, and the switch circuit is activated to cut off the The three-phase current loop achieves the purpose of detecting bus current and short-circuit protection. The device with bus current detection and short-circuit protection according to claim 13, wherein the current detection circuit can be formed by a shunt resistor or a current sensing element. The device with bus current detection and short-circuit protection according to claim 13, wherein the three-phase current is composed of current flowing through the three-phase power arm, and the three-phase power arm is composed of six power switches, Each of the two power switches forms a power arm of one phase. The device with bus current detection and short-circuit protection according to claim 13, wherein the low-frequency component current of the three-phase current is equivalent to the current flowing back to a ground terminal. The device with bus current detection and short circuit protection according to claim 13, wherein the switch circuit can be composed of a field effect transistor (Mosfet), a relay (Relay) or a power element. The device with bus current detection and short-circuit protection according to claim 13, wherein the signal processing circuit further includes: A low-pass filter is connected to the current detection circuit to filter out the high frequency AC signal component current of the voltage difference, leaving the low frequency signal component current. The device with bus current detection and short-circuit protection according to claim 13, wherein the signal processing circuit further includes: A high-pass filter is connected to the current detection circuit to filter out the low-frequency signal of the voltage difference Signal component current, leaving the high-frequency AC signal component current; A first integrator connected to the high-pass filter for integrating the current of the high-frequency AC signal component to generate the first integrated current; A second integrator connected to the high-pass filter for integrating the current of the high-frequency AC signal component to generate a second integrated current; A subtractor connected to the first integrator and the second integrator for subtracting the first integrated current and the second integrated current to generate the current rate of change; A first comparator connected to the first integrator to compare whether the first integrated current reaches the first critical value; A second comparator connected to the subtractor to compare whether the current change rate reaches the second critical value; and A gate is connected to the first comparator, the second comparator, and the switch circuit to determine when the first integral current reaches a first critical value and the current change rate reaches a second critical value. When all of them are satisfied, the output starts the switch circuit and cuts off the loop of the three-phase current. The device with bus current detection and short-circuit protection according to claim 13, wherein the first threshold value represents the absolute value of the set expected current. The device with bus current detection and short-circuit protection according to claim 13, wherein the second threshold value represents the current change rate within a time change.

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