TWI814206B - Method of clamping output current of three-phase power converter - Google Patents

Abstract

A method of clamping an output current of a three-phase power converter is provided. The three-phase power converter includes three switch bridge arms and provides a three-phase output voltage command, and each switch bridge arm has an upper switch and a lower switch connected in series. The method includes steps of: determining that the output current is greater than a first current threshold value to activate a current clamping control procedure, comparing a carrier signal to the three-phase output voltage command to turn on the lower switch by a first zero vector when the carrier signal is rising and to turn on the upper switch by a second zero vector when the carrier signal is falling, determining that the output current is greater than a second current threshold value, which is greater than the first current threshold value, to activate an over current protection procedure.

Description

Clamp control method of output current of three-phase power converter

The present invention relates to a method for controlling the output current of a power converter, and in particular to a method for clamping the output current of a three-phase power converter.

FIG. 1 is a system architecture diagram of a traditional motor driver, in which the motor 900 controls the load to be controlled through the driving of the power converter 100. See also FIG. 3. Figure 2 is a circuit diagram of a traditional three-phase power converter. The power converter 100 is composed of a three-arm structure composed of six switches (each including an upper arm switch _Su1 , S _v1 , _Sw1 and a lower arm switch _Su2 , S _v2 , _Sw2 ). Each phase output is connected to one arm. The center point of the upper and lower arm switches is a circuit structure that is known and widely used in industrial products.

In various industrial applications, a power converter 100 is often used to convert electric energy. As shown in Figure 3, the power converter 100 disposed between the AC side and the DC side converts the electric energy of the battery 200. , and provide power to the load 300. Here, the place where the power converter 100 is connected to the battery 200 can be called the "DC side", which can be a battery, a solar panel, a capacitor, etc. in different practical applications. The load side in Figure 3 can also be called the "AC side". In different practical applications, it can be motors, power grids, industrial products, etc.

Specifically, FIG. 3 is an architecture diagram of a pulse-width modulation (PWM) system applied to the power converter 100. According to different actual applications, the controller 400 corresponding to the power converter 100 will be designed in different ways. For example, when the load 300 is a voltage source, the power converter 100 is often used as an active front end. In this case, the controller 400 must adjust the power factor on the AC side. If the load 300 is a motor, the power converter 100 must be designed to control various types of motors. Therefore, with different application scenarios, the design of the controller 400 corresponding to the power converter 100 is also different, but the purpose is to control the voltage on the AC side to achieve the control purpose. Therefore, the controller 400 will generate a corresponding voltage command V _ref for the AC side output voltage that is desired to be controlled. Furthermore, the voltage command V _ref can be converted (modulated) through the pulse width modulation technology 500 to output a switching signal to the switching element module on the power converter 100 for switching to output a corresponding voltage. As shown in FIG. 3 , the output voltage of the power converter 100 is a voltage in the form of a pulse wave. Ideally, if there is no loss in the system, the average value of the pulse voltage will be the voltage command V _ref .

Most pulse width modulation technology used in traditional three-phase power converters is a switching method called vector space pulse width modulation (SVPWM). The method is to combine the voltage command of each phase of the three phases with a carrier ePWM compare. As shown in Figure 4, when the phase voltage command V _ref is greater than the carrier ePWM, the upper switch of the arm is turned on and the lower switch is turned off. As shown in Figure 5, if the three-phase voltage commands (v _u *, v _v *, v _w *) are compared with the carrier ePWM, the switches of each arm of the three phases can be sorted out as shown in Figure 5 (when v _u *>v _v *>v _w *), if you analyze various voltage command combinations and transfer their output voltages to the dq synchronization box, they can be organized into a space vector diagram composed of voltage vectors v ₀ -v ₇ (Space vector diagram), as shown in Figure 6. For example, v ₁ (100) means that the U-phase upper arm switch is turned on, and the V and W-phase lower arm switches are turned on. In addition, the output voltages generated by v ₀ (000) and v ₇ (111) are both zero, so they are called zero. vector, and the remaining v ₁ -v ₆ vectors are called active vectors. This PWM method has been widely used in various power converter products.

The basic concept of SVPWM can be explained from Figure 6: the three-phase voltage v _u *, v _v *, v _w * command is transferred to the synchronization frame to v*. During the frame transfer process, the angle θ between the voltage command v* and the q axis will be obtained. , different θ angles make v* fall within any vector triangle in Figure 6. This voltage command is synthesized by the voltage vectors that make up the triangle during a switching cycle. The voltage command v* at this time falls in the triangular interval composed of v ₁ , v ₂ , v ₀ /v _7. At this time, during a PWM switching cycle, as shown in Figure 5, the output voltage vector is v ₇ in sequence -v ₂ -v ₁ -v ₀ -v ₁ -v ₂ -v ₇ . Therefore, when the voltage command v* falls within any triangle interval in Figure 6, it is composed of two active vectors v _x , v _y and two zero sequence vectors v ₀ , v ₇ within the triangle. Table 1 defines the relationship between voltage range and angle.

However, in order to prevent overcurrent from damaging the components of the power converter, an overcurrent protection mechanism is usually designed in the motor driver system. To this end, how to design a control method for the output current of a power converter, especially a clamp control method for the output current of a three-phase power converter, to solve the problems and technical bottlenecks existing in the existing technology, is the inventor of this case. important topics studied.

The purpose of the present invention is to provide a method for controlling the output current of a power converter to solve the problems of the prior art.

In order to achieve the aforementioned purpose, the present invention proposes a method for controlling the output current of a power converter, in which the three-phase power converter includes three sets of switch bridge arms, and each set of switch bridge arms has an upper switch and a lower switch connected in series, and Provides three-phase output voltage commands. The clamping control method includes: (a) when it is determined that the output current is greater than the first current threshold, starting the current clamping control program; (b) comparing the carrier signal with the three-phase output voltage command, and when the carrier signal is in the rising interval, the switch is turned on under the control of the first zero vector, and when the carrier signal is in the falling interval, the upper switch is turned on under the control of the second zero vector; and (c) determine that the output current is greater than the second current threshold When , the overcurrent protection program is started, in which the second current threshold is greater than the first current threshold.

In one embodiment, in step (b), when the carrier signal reaches the peak value, the first zero vector is used to control the lower switch to turn on; when the carrier signal reaches the trough value, the second zero vector is used to control the upper switch to turn on.

In one embodiment, in step (c), the overcurrent protection program controls all upper switches and lower switches of the three groups of switch bridge arms to turn off.

In one embodiment, when the current clamp control procedure is executed, there are two different active vectors between the first zero vector and the second zero vector.

In one embodiment, the first zero vector is a vector used to control all the lower switches of the three sets of switch bridge arms to be turned on; the second zero vector is a vector used to control all the upper switches of the three sets of switch bridge arms to be turned on. vector.

In one embodiment, when the carrier signal reaches a peak value or a trough value, the current clamp control procedure is interrupted.

In one embodiment, when the carrier signal rises to the wave peak value, the interrupt current clamping control process is performed, and the switch is turned on under the first zero vector continuous control; when the carrier signal drops to the wave trough value, the interrupt current clamping control process is performed. The second zero vector continues to control the upper switch to be turned on.

In one embodiment, between step (b) and step (c), the method further includes: (d) when it is determined that the output current is greater than a third current threshold, initiating a second current clamp control procedure, wherein the third current threshold is greater than the third current threshold. A current threshold and less than the second current threshold.

In one embodiment, the second current clamping control process is executed by controlling the upper switch to turn off and the lower switch to turn off of the three groups of switch bridge arms.

In one embodiment, the load connected to the output of the three-phase power converter is a generator or a motor operating in generator mode.

In this way, the control method of the output current of the power converter proposed by the present invention can greatly reduce the vibration of the motor, significantly reduce the ripples of the output current, avoid the feedback of the output current (energy) to the DC side voltage side, and reduce the switching loss.

In order to further understand the technology, means and effects adopted by the present invention to achieve the intended purpose, please refer to the following detailed description and drawings of the present invention. It is believed that the purpose, features and characteristics of the present invention can be understood in depth and For specific understanding, however, the attached drawings are only for reference and illustration, and are not intended to limit the present invention.

100:Power converter

200:Battery

300:Load

400:Controller

500: Pulse width modulation technology

900: Motor

S _CC : Clamp current signal

S _CC1 : first clamp current signal

S _CC2 : Second clamp current signal

V _ref : voltage command

ePWM: carrier wave

S _u1 ,S _v1 ,S _w1 : upper arm switch

S _u2 ,S _v2 ,S _w2 : lower arm switch

i _u ,i _v ,i _w : output current

v _u *, v _v *, v _w *: three-phase voltage command

V _{ref_max} , V _{ref_mid} , V _{ref_min} : three-phase output voltage command

v _x , v _y , v ₁ ~ v ₆ : active vector

v ₀ , v ₇ : zero vector

S1~S2: steps

S11~S13: Steps

Figure 1: System architecture diagram of a traditional motor driver.

Figure 2: Circuit diagram of a traditional three-phase power converter.

Figure 3: It is a system architecture block diagram of pulse width modulation traditionally used in power converters.

Figure 4: It is a schematic waveform diagram of the PWM switching method of a traditional power converter.

Figure 5: It is a schematic waveform diagram of the SVPWM switching method of a traditional three-phase power converter.

Figure 6: It is a vector space diagram composed of voltage vectors under traditional SVPWM switching.

Figure 7: It is a schematic diagram of the current protection mechanism applied to the motor driver.

Figure 8: A schematic diagram of the current clamp control method.

Figure 9: Equivalent circuit diagram of a current clamp controlled three-phase power converter.

Figure 10: It is a schematic diagram of controlling all switches of the power converter to be closed.

Figure 11 is a schematic diagram of the present invention using zero vector to control the switch of the power converter.

Figure 12A: is a circuit diagram of the first embodiment of the power converter switching to zero vector.

Figure 12B is a circuit diagram of a second embodiment of the power converter switching to zero vector.

Figure 13 is a specific schematic diagram of the first embodiment of the present invention in which the switch of the power converter is controlled with zero vector.

Figure 14 is an equivalent circuit diagram of the present invention using zero vector to control the switch of the power converter.

Figure 15 is a specific schematic diagram of the second embodiment of the present invention for controlling the switch of the power converter with zero vector.

Figure 16 is a flow chart of the output current clamping control method of the three-phase power converter of the present invention.

The technical content and detailed description of the present invention are as follows with reference to the drawings.

As mentioned above, in order to prevent overcurrent from damaging the components of the power converter, an overcurrent protection mechanism is usually designed in the motor driver system, as shown in Figure 7, which is the current protection mechanism applied to the motor driver. Schematic diagram. The system's hardware or firmware will feedback the output currents i _u , i _v , and i _w to determine the current magnitude. When any phase output current i _u , _iv , i _w is instantly greater than the upper limit current value or exceeds the over-current protection command (that is, the judgment in step S2 is "yes"), the power converter 100 enters over-current protection and will All switches of the power converter 100 are turned off and the system stops operating.

But sometimes the motor load only undergoes a sudden transient change (such as instantaneous loading, instantaneous load loss or controller failure). After the sudden transient change has passed, the output current i _u , i _v , i _w can be stably output. . However, this over-current protection mechanism limits the operating flexibility of the power converter 100 . Therefore, in order to increase the operating range of the motor driver, a "clamping current control" is added to the protection mechanism to assist the power converter 100 in overcurrent transients. That is to say, when any phase output current i _u , _iv , i _w is instantly greater than the clamping current value or exceeds the clamping current protection command (that is, the judgment of step S1 is "yes"), the power converter 100 will not Directly enter the over-current protection. In other words, when the output current i _u , i _v , i _w is less than the upper limit current value or does not exceed the over-current protection command (that is, the judgment of step S2 is "No"), the power converter 100 will enter Clamp current control is used to suppress the magnitude of the output currents i _u , _iv , and i _w without temporarily turning off all switches of the power converter 100 and preventing the system from shutting down, thereby increasing the operating range of the power converter 100 and enabling Survive certain transient operations. However, if the current clamp control still cannot suppress the output currents i _u , _iv , and i _w , the system will still enter over-current protection.

The current clamp control method is shown in Figure 8. In the figure, the three-phase voltage commands (or three-phase output voltage commands) are V _{ref_max} , V _{ref_mid} , and V _{ref_min} in order of the maximum value, the middle value, and the minimum value, respectively. The triangular wave (carrier wave) is compared to generate a PWM signal. Each switching cycle is composed of two active vectors v _x , v _y and zero (sequence) vectors v ₀ , v ₇ . Referring to Figure 7, when the output current i _u , _iv , and i _w of any phase of the detection system exceeds the clamping current value (that is, the judgment of step S1 is "yes"), the current protection system will generate a clamping current signal ( clamping current signal)S _CC to the controller. When the controller receives the clamping current signal S _CC , such as the flag signal marked with an arrow in Figure 8, it will immediately turn off all switching signals (Gate off). As shown in Figure 10, when the first or third flag signal takes effect, it immediately enters the Gate off state at the active vector v _x . If the (second) flag signal occurs during the Gate off state, the Gate off state will continue to be maintained.

S _INTR shown in Figure 8 is the interrupt signal of the controller. It is usually generated at the peak or trough of a switching cycle and is used to reset the flag signal of the clamping current signal S _CC . . When the controller receives the interrupt signal S _INTR , it will make another judgment on the output current. If it is judged that the current is still greater than the clamping current value, it will continue to maintain the clamping current control to continue to suppress the output current. On the other hand, if it is determined that the current size is less than the clamping current value (because of the suppression by the clamping current control), the interrupt operation at the peak or valley will switch back to the normal operation of the PWM output. The equivalent circuit at this time is as follows: As shown in Figure 9. If the current flow direction is i _u <0, i _v >0, i _w >0, then the corresponding back-connected diode (rather than the upper and lower switches) is discharged according to the current flow to achieve the output current. However, the line-to-line cross-voltage on the motor side causes the DC side voltage V _dc to fluctuate greatly, such as jumping from +V _dc to -V _dc or from -V _dc to +V _dc , which will cause the output The side current has large current ripples, causing the mechanical motor to vibrate greatly.

Furthermore, by turning off all switches to achieve output current suppression, another phenomenon that will occur is that the output current (energy) is fed back to the DC side voltage side. This will cause the DC side voltage to increase, which will trigger the overcurrent. voltage protection.

Please refer to FIG. 16 , which is a flow chart of the output current clamping control method of the three-phase power converter of the present invention. The three-phase power converter includes three sets of switch arms, and each set of switch arms has an upper switch and a lower switch connected in series and provides three-phase output voltage commands. The steps of the clamp control method are detailed as follows.

First, when it is determined that the output current is greater than the first current threshold, the current clamp control program is started (S11). As mentioned before, the clamping current control method has a large cross-voltage on the output side of the motor, which can easily increase the motor current ripple and cause the motor to vibrate. Therefore, the clamp control method of the output current of the three-phase power converter proposed by the present invention does not use the method of closing all the switches of the power converter (as shown in Figure 10), but switches the power converter 100 to zero. vector (as shown in Figure 11). Specifically, as shown in Figure 11, when the controller receives the first flag signal of the clamping current signal S _CC , it uses the first zero vector v ₀ to control the upper and lower switches of the three-phase bridge arm, which means , controlling all lower switches to be turned on and all upper switches to be turned off, instead of controlling all upper and lower switches to be turned off. Similarly, when the controller receives the second flag signal of the clamping current signal S _CC , it uses the second zero vector v ₇ to control all upper switches to be turned on and all lower switches to be turned off. It is worth mentioning that with reference to Figure 13, when the carrier signal rises to the peak value of the wave, the current clamp control process is interrupted. The switch is turned on under the continuous control of the first zero vector v ₀ , and when the carrier signal drops to the bottom value, the interrupt is carried out. In the current clamp control program, the second zero vector v ₇ continues to control the conduction of the upper switch, which can reduce switching losses.

At this time, the equivalent circuit is as shown in FIG. 12A and FIG. 12B , where FIG. 12A shows the power converter 100 switching to the zero vector v ₇ , and FIG. 12B shows the power converter 100 switching to the zero vector v ₀ . Since the current flows inside the power converter 100, the output current can be suppressed, and the output current (energy) can be prevented from being fed back to the DC side voltage side. At this time, the output voltage of the motor 900 is zero when the line-to-line cross-voltage is zero vector, which greatly reduces the ripple of the output current, so that the vibration of the motor 900 can be greatly reduced even under the clamp current control operation.

Then, compare the carrier signal with the three-phase output voltage command, and when the carrier signal is in the rising interval, the switch is turned on under the control of the first zero vector, and when the carrier signal is in the falling interval, the switch is turned on under the control of the second zero vector (S12) . The zero vector switching method can be seen in Figure 6. There are two switching methods: zero vector v ₀ and zero vector v ₇ . As shown in Figure 5, the zero vector at the peak of the carrier wave is v ₀ , and the zero vector at the trough of the carrier wave is v ₇ . Furthermore, in order to reduce the switching loss during the current clamp control period, when the clamp current signal S _CC is the carrier signal rising from the trough to the peak (i.e., the rising interval or rising section) (i.e., the first flag signal), Then the clamp current control will select the zero vector v ₀ . On the contrary, when the clamping current signal S _CC is the carrier signal falling from the peak to the trough (i.e., the falling interval or section) (i.e., the second flag signal), the clamping current control will select the zero vector v ₇ .

Please refer to FIG. 13 , which is a detailed schematic diagram of the first embodiment of the present invention using zero vector to control the switch of the power converter. The voltage vector of the switch is determined by comparing the three-phase voltage command (V _{ref_max} , V _{ref_mid} , V _{ref_min} ) with the carrier wave. In FIG. 13 , the three-phase voltage commands are classified into voltage commands with a maximum value (V _{ref_max} ), a middle value (V _{ref_mid} ), and a minimum value (V _{ref_min} ). When the clamping current signal S _CC is detected, if the carrier signal is in the rising range or rising section, all three-phase voltage commands are clamped to the minimum voltage command (V _{ref_min} ), and the zero vector v ₀ can be generated. On the other hand, when the clamping current signal S _CC is detected, if all three-phase voltage commands are clamped to the maximum voltage command (V _{ref_max} ) when the carrier signal is in the falling interval or falling section, the zero vector v can be generated ₇ .

As mentioned above, the clamp control method of the output current of the three-phase power converter proposed by the present invention mainly uses a zero vector instead of fully closing the switch of the power converter to reduce the ripple of the output current. However, this method This is only applicable if the motor operates in the "motor" mode. If the motor operates in the "generator" mode at this time, using zero vector operation cannot reduce the output current ripple. In this case, the power must still be All switches of the converter are turned off, allowing the energy on the AC side to be poured into the braking resistor R _dc on the DC side for consumption, thereby reducing the AC current, as shown in Figure 14.

However, for the motor driver, it is not necessarily possible to know whether the motor is currently operating in the "motor" mode or the "generator" mode. Therefore, the clamping current control strategy can be implemented through two Clamping current signals, such as the first clamping current signal S _CC1 and the second clamping current signal S _CC2 , are used as the basis for determination, as shown in Figure 15 . Specifically, if the magnitude of the output current i _u , _iv , i _w exceeds the first current threshold, where the first current threshold corresponds to the first clamping current signal S _CC1 used for judgment, that is, if the output current When the magnitudes of i _u , _iv , and i _w exceed the first clamping current signal S _CC1 , switch to the zero vector according to the aforementioned method. If the motor operates in the "motor" mode, the magnitude of the output current i _u , i _v , i _w can be suppressed, so the output current i _u , i _v , i _w will gradually converge, and a smaller current can be output ripples. On the contrary, when the motor operates in the "generator" mode, the output currents i _u , _iv , and i _w will continue to increase. In other words, when the motor operates in the "generator" mode, the output currents i _u , _iv , and i _w cannot be effectively suppressed through a single current clamp control process.

Therefore, this case can further provide a second current clamp control program, which is to further execute the current clamp control program, so that when the magnitudes of the output currents i _u , _iv , and i _w exceed the first current threshold, but after When the zero vector operation still cannot reduce the ripples of the output currents i _u , _iv , and i _w , the second current clamp control program is started. Specifically, it is further determined that when the output current i _u , _iv , and i _w is greater than the third current threshold, in which the third current threshold is greater than the first current threshold, the upper switches of the three sets of switch bridge arms are controlled to turn off and The lower switches are turned off, in other words, by turning off all switches of the power converter, the energy on the AC side is poured into the braking resistor R _dc on the DC side for consumption, thereby reducing the AC current.

Finally, when it is determined that the output current is greater than the second current threshold, the overcurrent protection program is started (S13). The second current threshold is greater than the first current threshold (also greater than the third current threshold), and the second current threshold corresponds to the second clamping current signal S _CC2 used for judgment. When the magnitude of the output current i _u , _iv , i _w exceeds the second current threshold, that is, when the magnitude of the output current i _u , _iv , i _w exceeds the second clamping current signal S _CC2 , it represents the aforementioned two stages. None of the current clamp control programs can effectively suppress the output currents i _u , _iv , and i _w , then the power converter 100 enters over-current protection, which will cut off all switches of the power converter 100 and stop the system, thus reaching The purpose of reducing the output current.

To sum up, the present invention has the following features and advantages:

1. The clamp control method of the output current of the three-phase power converter proposed by the present invention does not use the strategy of turning off all the switches of the power converter, but switches the power converter to the zero vector, so that even if the motor is clamped Under current control operation, vibration can be greatly reduced.

2. The clamp control method proposed in the present invention uses the zero vector to reduce the cross-voltage of the output voltage, thereby significantly reducing the ripple of the output current.

3. The clamp control method proposed in the present invention can not only suppress the output current, but also prevent the output current (energy) from being fed back to the DC side voltage side.

4. When the carrier signal rises to the peak value or drops to the trough value, the current clamping control process is interrupted. The same zero vector continues to control the switch conduction, which can reduce switching losses.

The above are only detailed descriptions and drawings of the preferred embodiments of the present invention. However, the characteristics of the present invention are not limited thereto and are not used to limit the present invention. The entire scope of the present invention should be determined by the following patent application scope. Subject to the present invention, all embodiments that are within the spirit of the patentable scope of the present invention and similar changes thereof shall be included in the scope of the present invention. Any person familiar with the art can easily think of such changes or modifications in the field of the present invention. Modifications may be covered by the following patent scope of this case.

S11~S13: Steps

Claims (10)

A clamping control method for the output current of a three-phase power converter. The three-phase power converter includes three sets of switch bridge arms, and each set of switch bridge arms has an upper switch and a lower switch connected in series, and provides a three-phase output. voltage command, the clamp control method includes: (a) when it is determined that the output current is greater than a first current threshold, starting a current clamp control process; (b) comparing a carrier signal with the three-phase output voltage command, and In the rising interval of the carrier signal, a first zero vector is used to control the conduction of the lower switches, and in the falling interval of the carrier signal, a second zero vector is used to control the conduction of the upper switches; and (c) determine the output current When it is greater than a second current threshold, an overcurrent protection program is started, wherein the second current threshold is greater than the first current threshold. The clamp control method as described in claim 1, wherein in step (b), when the carrier signal reaches a peak value, the first zero vector is used to control the lower switches to turn on; when the carrier signal reaches a valley value When , the second zero vector is used to control the upper switches to turn on. The clamp control method as described in claim 1, wherein in step (c), the over-current protection program controls all the upper switches and the lower switches of the three groups of switch bridge arms to turn off. The clamp control method of claim 1, wherein when the current clamp control program is executed, there are two different active vectors between the first zero vector and the second zero vector. The clamp control method as described in claim 1, wherein the first zero vector is a vector used to control all the lower switches of the three sets of switch bridge arms to be turned on; the second zero vector is a vector used to control The vector at which all the upper switches of the three sets of switch bridge arms are turned on. The clamp control method as described in claim 1, wherein in step (b), when the carrier signal reaches a peak value or a valley value, the current clamp control program is interrupted. The clamp control method as described in claim 6, wherein in step (b), when the carrier signal rises to the peak value of the wave, the current clamp control procedure is interrupted, and the first zero vector continues to control the lower switches. Turn on; when the carrier signal drops to the valley value, the current clamp control process is interrupted, and the second zero vector continues to control the upper switches to turn on. The clamp control method as described in claim 1, further comprising: (d) when it is determined that the output current is greater than a third current threshold, activating a second current clamp between steps (b) and (c). A control program, wherein the third current threshold is greater than the first current threshold and less than the second current threshold. The clamp control method as described in claim 8, wherein the second current clamp control program is executed by controlling the upper switches to turn off and the lower switches to turn off of the three sets of switch bridge arms. The clamp control method of claim 8, wherein a load connected to the output of the three-phase power converter is a generator or a motor operating in a generator mode.

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