阅读说明：本技术 变频控制方法及变频控制装置、超高速永磁同步电机的控制方法 (Frequency conversion control method and device and control method of ultra-high-speed permanent magnet synchronous motor ) 是由 许柳 李燕 赵文超 于 2020-06-28 设计创作，主要内容包括：本发明提供一种变频控制方法及变频控制装置、超高速永磁同步电机的控制方法,该变频控制方法应用于变频控制装置,该变频控制装置包括直流斩波电路以及逆变电路,该方法包括获取永磁同步电机的实际频率,根据实际频率与永磁同步电机运行的目标频率计算母线调节电压,根据母线调节电压调节直流斩波电路的两个第一开关器件的导通时间；根据目标频率向逆变电路中的第二开关器件加载控制信号,在变频控制装置的输出频率的一个周期内,每一第二开关器件的开关状态切换一次。该变频控制装置用于实现上述的变频控制方法。本发明可以满足超高速变频设备的控制要求,且第二开关器件的开关频率较低,降低变频控制装置的成本。(The invention provides a frequency conversion control method, a frequency conversion control device and a control method of an ultra-high-speed permanent magnet synchronous motor, wherein the frequency conversion control method is applied to the frequency conversion control device, the frequency conversion control device comprises a direct current chopper circuit and an inverter circuit, the method comprises the steps of obtaining the actual frequency of the permanent magnet synchronous motor, calculating the bus regulating voltage according to the actual frequency and the target frequency of the operation of the permanent magnet synchronous motor, and regulating the conducting time of two first switching devices of the direct current chopper circuit according to the bus regulating voltage; and loading a control signal to a second switching device in the inverter circuit according to the target frequency, and switching the switching state of each second switching device once in one period of the output frequency of the variable frequency control device. The frequency conversion control device is used for realizing the frequency conversion control method. The invention can meet the control requirement of ultra-high-speed frequency conversion equipment, and the switching frequency of the second switching element is lower, thereby reducing the cost of the frequency conversion control device.)

1. The frequency conversion control method is applied to a frequency conversion control device, and the frequency conversion control device comprises a direct current chopper circuit and an inverter circuit;

the method is characterized by comprising the following steps:

acquiring the actual frequency of controlled variable frequency equipment, calculating a bus regulation voltage according to the actual frequency and the target frequency of the controlled variable frequency equipment, and regulating the conduction time of two first switching devices of the direct current chopper circuit according to the bus regulation voltage;

and loading a control signal to a second switching device in the inverter circuit according to the target frequency, and switching the switching state of each second switching device once in one period of the output frequency of the variable frequency control device.

2. The frequency conversion control method according to claim 1, characterized in that:

calculating the bus bar regulation voltage according to the actual frequency and the target frequency comprises: and calculating the bus regulating voltage according to the actual frequency and the target frequency by applying a proportional-integral algorithm.

3. The frequency conversion control method according to claim 2, characterized in that:

calculating the bus bar regulation voltage according to the actual frequency and the target frequency by applying a proportional-integral algorithm comprises: and calculating a difference value between the target frequency and the actual frequency, and calculating the bus regulating voltage according to the difference value by applying a proportional-integral algorithm.

4. The frequency conversion control method according to claim 3, characterized in that:

calculating the bus regulation voltage from the difference value using a proportional-integral algorithm comprises: and calculating the bus calculation voltage according to the difference value by applying a proportional-integral algorithm, wherein the bus regulation voltage is the product of the bus calculation voltage and a preset regulation parameter.

5. The variable frequency control method according to any one of claims 1 to 4, characterized in that:

adjusting the conduction time of the two first switching devices according to the bus bar regulation voltage comprises: and voltage and current double-loop control is carried out by applying the bus adjusting voltage to obtain a modulation voltage, and the modulation voltage is applied to form pulse modulation signals loaded to the two first switching devices.

6. The frequency conversion control method according to claim 5, characterized in that:

obtaining a modulation voltage after voltage and current double-loop control by applying the bus regulation voltage comprises: and performing first proportional integral calculation by using the bus regulating voltage and the actual bus voltage to obtain a target current, and performing second proportional integral calculation by using the target current and the actual current to obtain the modulation voltage.

7. The variable frequency control method according to any one of claims 1 to 4, characterized in that:

the inverter circuit comprises three bridge arms, and each bridge arm is provided with two second switching devices;

the control signal applied to the second switching device is a six-step control signal.

8. The frequency conversion control method according to claim 7, characterized in that:

in one period of the output frequency of the variable frequency control device, the conducting phase angle of each second switching device is 180 degrees.

9. The control method of the ultra-high speed permanent magnet synchronous motor is characterized by comprising the following steps:

the method for controlling the frequency conversion according to any one of claims 1 to 8 is applied to control the permanent magnet synchronous motor, wherein the controlled frequency conversion equipment is the permanent magnet synchronous motor.

10. Frequency conversion control device, its characterized in that includes:

the direct current chopper circuit is provided with two first switching devices which are connected in series, and bus regulation voltage output by the direct current chopper circuit is loaded to two ends of the inverter circuit;

the inverter circuit is provided with a plurality of second switching devices, and the second switching devices output driving signals to controlled frequency conversion equipment;

the direct-current chopper circuit is used for regulating the conduction time of the two first switching devices according to the bus regulation voltage obtained by calculating the actual frequency and the target frequency of the controlled variable-frequency equipment;

the inverter circuit is used for loading a control signal to the second switching device according to the target frequency, and the switching state of each second switching device is switched once in one period of the output frequency of the variable frequency control device.

11. The variable frequency control device according to claim 10, wherein:

the direct current chopper circuit further includes an inductor, and one end of the inductor is connected to a connection of the two first switching devices.

12. The variable frequency control device according to claim 10 or 11, wherein:

two first switching devices are connected in series to form a chopping branch circuit;

the direct-current chopper circuit further comprises a capacitor, and two ends of the capacitor are connected to two ends of the chopping branch circuit.

13. The variable frequency control device according to claim 10 or 11, wherein:

the inverter circuit is provided with three bridge arms, and each bridge arm is provided with two second switching devices;

the control signal applied to the second switching device is a six-step control signal.

14. The variable frequency control device according to claim 10 or 11, wherein:

the first switching device and/or the second switching device is an insulated gate bipolar transistor.

Technical Field

The invention relates to the field of motor control, in particular to a frequency conversion control method and a frequency conversion control device for realizing the method, and also relates to a control method of an ultra-high-speed permanent magnet synchronous motor for controlling the ultra-high-speed permanent magnet synchronous motor by applying the frequency conversion control method.

Background

With the development of machining technology, more and more machine tools are configured with ultra-high-speed motors, because the rotating speed of the ultra-high-speed motor is much higher than that of a conventional motor, and the ultra-high-speed motor has high power density, small rotational inertia and fast dynamic response, more and more attention is paid, and the technical development of the ultra-high-speed motor also becomes the research focus of researchers.

The rotation speed of the super-high speed motor can reach hundreds of thousands of revolutions per minute, and the highest output frequency can reach more than 2 kHz. An ultra-high speed permanent magnet synchronous motor is a typical ultra-high speed motor, and the motor is generally provided with a plurality of switching tubes, such as Insulated Gate Bipolar Transistors (IGBTs), through which driving signals are output to the ultra-high speed permanent magnet synchronous motor. In order to load a current to the ultra-high-speed permanent magnet synchronous motor as a relatively ideal sine wave signal, the PWM modulation signal described in each switching tube needs to have an extremely high switching frequency, and for example, the ideal switching frequency needs to be 25kHz or higher.

However, the conventional igbt is limited by the highest operating frequency of the switching device, so that the switching frequency and the power requirement can hardly be achieved at the same time, and the igbt is easily damaged by an excessively high switching frequency. In addition, in order to output the PWM signals with extremely high frequency to each switching tube, the processor needs to adopt a relatively complex control algorithm, that is, an extremely high requirement is provided for the operating speed of the processor, but the operating speed of the currently commonly used processor, such as a DSP processor, is difficult to reach the requirement of generating the PWM signals with extremely high frequency, the requirement of fast dynamic response of the ultra-high speed permanent magnet synchronous motor is difficult to meet, and the processor has problems in the aspects of accuracy and rapidity of control.

In order to solve the above problems, some researchers have proposed corresponding solutions, for example, chinese patent application No. CN201710169900.2 proposes a driving controller for a high-speed motor, in which 6 common igbt bipolar crystals in an inverter are replaced with an igbt bipolar crystal made of SiC material, and the igbt bipolar crystal made of SiC material has low on-resistance and can endure higher environmental temperature, reduce the volume of a heat sink and power loss, and improve the efficiency and power density of the driving controller for a high-speed motor. However, the cost of the SiC material of the igbt is very high, which results in high implementation cost of this solution, and the design of the driving protection circuit of the hardware circuit is more complicated.

Because the rotating speed of the ultra-high-speed permanent magnet synchronous motor is high and the speed regulation range is wider, if the motor is controlled by applying the method, the generated harmonic frequency is very close to the fundamental frequency of the motor, and the harmonic of the power supply system of the ultra-high-speed permanent magnet synchronous motor is larger, so that the suppression of the harmonic current of the power supply system of the ultra-high-speed permanent magnet synchronous motor is very difficult at the moment. Thus, in this prior art solution, the PWM inverter would not be suitable for the control of an ultra-high speed permanent magnet synchronous motor.

Disclosure of Invention

The first purpose of the invention is to provide a frequency conversion control method which has low cost and is controlled by a PWM signal with lower frequency.

The second purpose of the invention is to provide a variable frequency control device for realizing the variable frequency control method.

The third purpose of the invention is to provide a control method of the ultra-high speed permanent magnet synchronous motor applying the frequency conversion control method.

In order to achieve the first object of the present invention, the frequency conversion control method provided by the present invention is applied to a frequency conversion control device, and the frequency conversion control device comprises a direct current chopper circuit and an inverter circuit; the method comprises the following steps: acquiring the actual frequency of the permanent magnet synchronous motor, calculating the bus regulation voltage according to the actual frequency and the target frequency of the permanent magnet synchronous motor, and regulating the conduction time of two first switching devices of the direct current chopper circuit according to the bus regulation voltage; and loading a control signal to a second switching device in the inverter circuit according to the target frequency, and switching the switching state of each second switching device once in one period of the output frequency of the variable frequency control device.

As can be seen from the above solution, the present invention implements the control of the bus voltage through the single closed loop control of the frequency, and adjusts the output frequency of the motor according to the relationship between the bus voltage and the output frequency of the motor, that is, adjusts the output frequency of the motor by adjusting the bus voltage, rather than changing the frequency of the motor by controlling the frequency of the PWM signal applied to each second switching device, so that the frequency of the control signal applied to each second switching device is low. Therefore, the invention does not need to adopt an insulated gate bipolar transistor made of SiC and other materials to meet the requirement of extremely high switching frequency, and can realize the rotating speed of hundreds of thousands of revolutions per minute of the ultra-high-speed motor by only adjusting the bus voltage.

Further, since the frequency of the PWM signal applied to the second switching device is low, the harmonic content at the fundamental frequency can be reduced. And because the frequency of the PWM signal is low, the PWM signal can be generated by adopting a common processor, the program executed by the processor is simple, the time required for generating the PWM signal is shorter, namely the execution time of the processor is shortened, and the response speed of the processor is improved.

Preferably, the calculating the bus bar regulating voltage according to the actual frequency and the target frequency comprises: and calculating the bus regulating voltage according to the actual frequency and the target frequency by applying a proportional-integral algorithm.

Because the proportional-integral algorithm is a common and mature algorithm, the bus regulating voltage is calculated through the proportional-integral algorithm, on one hand, the difficulty of computer program development is reduced, and on the other hand, the running program of the processor is simpler and the response speed is higher.

Further, the step of calculating the bus regulating voltage according to the actual frequency and the target frequency by applying a proportional-integral algorithm comprises the following steps: and further, calculating the bus calculation voltage according to the difference by using a proportional integral algorithm, wherein the bus adjustment voltage is the product of the bus calculation voltage and a preset adjustment parameter.

Therefore, the calculation of the bus adjusting voltage is simple, the calculation amount of the processor is small, the response speed of the processor is high in the process of controlling the ultra-high-speed permanent magnet synchronous motor, and the frequency of the motor can be controlled effectively and accurately.

In a further aspect, adjusting the conduction time of the two first switching devices according to the bus bar regulation voltage includes: and voltage and current double-loop control is carried out by using the bus regulating voltage to obtain a modulation voltage, and the modulation voltage is used for forming pulse modulation signals loaded to the two first switching devices.

Therefore, after the bus regulating voltage is obtained through calculation, PWM signals loaded to the two first switching devices are calculated according to the bus regulating voltage, so that the terminal voltage of the ultra-high-speed permanent magnet synchronous motor is controlled, the rotating speed of the motor is further controlled, and the ultra-high-speed permanent magnet synchronous motor runs according to the preset frequency.

Further, the step of obtaining the modulation voltage after the voltage and current double-loop control by using the bus regulation voltage comprises: and performing first proportional integral calculation by using the bus regulating voltage and the actual voltage of the bus to obtain a target current, and performing second proportional integral calculation by using the target current and the actual current to obtain a modulation voltage.

Therefore, the voltage and current double-loop control is a common motor control mode, and the modulation voltage is controlled and calculated through the voltage and current double-loop control, so that the calculation difficulty of the modulation voltage is reduced.

The inverter circuit further comprises three bridge arms, and each bridge arm is provided with two second switching devices; the control signal applied to the second switching device is a six-step control signal.

Therefore, the control signals of the second switching devices loaded on the three bridge arms are six-step control signals, so that the switching state of each second switching device can be ensured to be switched only once in one period of the output frequency, the switching frequency of the second switching devices is greatly reduced, and the expensive insulated gate bipolar transistor made of SiC materials is avoided being used as the second switching device.

Further, in a period of the output frequency of the variable frequency control device, the conducting phase angle of each second switching device is 180 °.

Therefore, in one period, the on-time and the off-time of each second switch device are equal, and by matching with the six-step control signal, the on-off frequency of the second switch device is very low, no high-frequency harmonic signal is generated, and the working requirement can be met by using a common insulated gate bipolar transistor.

In order to achieve the second purpose, the frequency conversion control device provided by the invention comprises a direct current chopper circuit and an inverter circuit, wherein the direct current chopper circuit is provided with two first switching devices which are connected in series, and the bus regulation voltage output by the direct current chopper circuit is loaded to two ends of the inverter circuit; the inverter circuit is provided with a plurality of second switching devices which output driving signals to the permanent magnet synchronous motor; the direct-current chopper circuit is used for adjusting the conduction time of the two first switching devices according to the bus adjusting voltage obtained by calculating the actual frequency and the target frequency of the permanent magnet synchronous motor; the inverter circuit is used for loading a control signal to the second switching device according to the target frequency, and the switching state of each second switching device is switched once in one period of the output target frequency of the variable frequency control device.

As can be seen from the above-mentioned solution, the control of the bus voltage is realized by the single closed loop control of the frequency, and the output frequency of the motor is adjusted according to the relationship between the bus voltage and the output frequency of the motor, that is, the output frequency of the motor is adjusted by adjusting the bus voltage, rather than changing the frequency of the motor by controlling the frequency of the PWM signal applied to the plurality of second switching devices, and therefore, the frequency of the control signal applied to each second switching device is low. In this way, the second switch device can be implemented using a common insulated gate bipolar transistor without using a high-priced insulated gate bipolar transistor made of SiC or the like to meet the requirement of extremely high switching frequency. In addition, the invention can realize the rotating speed of the ultra-high speed motor of hundreds of thousands of revolutions per minute only by adjusting the bus voltage, and can avoid generating high-frequency harmonic signals.

Preferably, the dc chopper circuit further includes an inductor, and one end of the inductor is connected to a connection point of the two first switching devices.

The further scheme is that two first switching devices are connected in series to form a chopping branch circuit; the direct current chopper circuit further comprises a capacitor, and two ends of the capacitor are connected to two ends of the chopper branch.

Therefore, the capacitor has a voltage stabilizing effect on the voltage of the chopping branch circuit, and the stability of the voltage loaded to the inverter circuit is ensured, so that the running stability of the ultra-high-speed permanent magnet synchronous motor is improved.

The inverter circuit is further provided with three bridge arms, and each bridge arm is provided with two second switching devices; the control signal applied to the second switching device is a six-step control signal.

In a further aspect, the first switching device and/or the second switching device is an insulated gate bipolar transistor.

In order to achieve the third objective, the control method of the ultra-high speed permanent magnet synchronous motor provided by the invention applies the frequency conversion control method to control the ultra-high speed permanent magnet synchronous motor, and the controlled frequency conversion device is a permanent magnet synchronous motor.

Drawings

Fig. 1 is an electrical schematic diagram of an embodiment of the variable frequency control apparatus of the present invention.

Fig. 2 is a graph of terminal voltage and frequency during constant torque control operation of the motor.

Fig. 3 is a control schematic block diagram of an embodiment of the frequency conversion control method of the present invention.

Fig. 4 is a control schematic block diagram for calculating the bus regulation voltage in the embodiment of the frequency conversion control method of the present invention.

Fig. 5 is a control schematic block diagram for calculating a pulse modulation signal applied to a first switching device in an embodiment of the variable frequency control method of the present invention.

FIG. 6 is a waveform diagram of phase voltages and line voltages of two phase coils in the embodiment of the variable frequency control method of the present invention.

The invention is further explained with reference to the drawings and the embodiments.

Detailed Description

The frequency conversion control method is applied to a frequency conversion control device, and the frequency conversion control device is used for controlling the ultra-high-speed permanent magnet synchronous motor. The ultra-high speed permanent magnet synchronous motor can be applied to industrial equipment such as machine tools and the like.

Frequency conversion control device embodiment:

referring to fig. 1, the present embodiment has a dc chopper circuit 11 and an inverter circuit 12, and the dc chopper circuit 11 receives a dc voltage source U_dA dc voltage is supplied and has an inductor L1, two first switching devices T1, T2, preferably two first switching devices T1, T2 connected in series and forming a chopping branch, each first switching device being connected in parallel with a diode, for example first switching device T1 in parallel with diode D1, first switching device T2 in parallel with diode D2. The dc chopper circuit 11 further has a capacitor C1, and the capacitor C1 is connected in parallel with the chopping branch, that is, two ends of the capacitor C1 are respectively connected to two ends of the chopping branch.

As can be seen from fig. 1, one end of inductor L1 is connected to dc voltage source U_dThe other end of the inductor L1 is connected to the junction of the two first switching devices T1, T2. Preferably, both of the first switching devices T1, T2 are Insulated Gate Bipolar Transistors (IGBTs), and are not insulated gate bipolar transistors made of SiC material.

The voltage output by the dc chopper circuit 11 is applied to two ends of the inverter circuit 12, the inverter circuit 12 has three legs, each leg has two second switching devices connected in series, for example, the first leg includes the second switching devices T3 and T4, the second leg includes the second switching devices T5 and T6, and the third leg includes the second switching devices T7 and T8. And, each second switching device is connected in parallel with a diode, e.g., second switching device T3 is connected in parallel with diode D3, second switching device T4 is connected in parallel with diode D4, and so on.

Three bridge arms of the inverter circuit 12 correspond to three-phase coils of the permanent magnet synchronous motor 10, for example, a first bridge arm composed of second switching devices T3 and T4 corresponds to an a-phase coil of the permanent magnet synchronous motor 10, a second bridge arm composed of second switching devices T5 and T6 corresponds to a b-phase coil of the permanent magnet synchronous motor 10, a third bridge arm composed of second switching devices T7 and T8 corresponds to a c-phase coil of the permanent magnet synchronous motor 10, and the second switching device of each bridge arm controls a current signal loaded to each phase coil, so that the permanent magnet synchronous motor 10 is driven to operate.

In the present embodiment, the frequency of the permanent magnet synchronous motor 10 is controlled by controlling the voltage of the dc chopper circuit 11. As the terminal voltage and the frequency of the motor meet the corresponding V/f curve in the constant torque control operation process of the motor, as shown in figure 2, Us is the terminal voltage of the permanent magnet synchronous motor 10, f₁Is the frequency of the permanent magnet synchronous machine 10. It can be seen that the frequency and the terminal voltage of the permanent magnet synchronous motor 10 satisfy a certain relationship, for example, a linear relationship within a certain range, and therefore, the present embodiment controls the frequency of the permanent magnet synchronous motor 10, that is, controls the rotation speed of the permanent magnet synchronous motor 10 by controlling the terminal voltage of the permanent magnet synchronous motor 10. In addition, in order to avoid the switching frequency of the second switching device being too high, the present embodiment controls the second switching device by using a six-step control signal, and the switching state of each second switching device is cut off only once in one cycle of the output frequency of the ultra-high speed permanent magnet synchronous motor.

The embodiment of a frequency conversion control method and the embodiment of a control method of an ultra-high speed permanent magnet synchronous motor comprise the following steps:

the following describes the frequency conversion control method in detail with reference to fig. 3 to 6. In the embodiment, the control of the motor frequency is mainly realized by controlling the terminal voltage of the permanent magnet synchronous motor 10, and since the terminal voltage of the motor is obtained by reducing the bus voltage, the embodiment realizes the regulation of the terminal voltage by regulating the bus voltage, that is, realizes the control of the motor frequency by controlling the bus voltage of the permanent magnet synchronous motor 10. Specifically, the bus voltage is adjusted by the dc chopper circuit 11, that is, by controlling the on time of the two first switching devices T1 and T2.

In addition, the switching frequency of the switching state of each second switching device of the inverter circuit 12 is the electrical frequency of the motor, and the switching state of each second switching device of the inverter circuit 12 is only switched once in each cycle of the output frequency of the variable frequency control device, that is, the on and off states are only switched once, and for a motor of hundreds of thousands of revolutions per minute, the operating frequency of the second switching device is low, so that the requirement can be met by only adopting a common insulated gate bipolar transistor without using an expensive SiC insulated gate bipolar transistor.

The frequency control of the permanent magnet synchronous motor 10 is realized by adjusting the bus voltage, the frequency of the motor is controlled by using the V/f curve shown in fig. 2, namely the relationship between the terminal voltage and the frequency, although the method is a simpler control method, the method performs open-loop control on the rotating speed of the motor, the dynamic characteristic of the rotating speed of the motor is poor, the utilization rate of the torque of the motor is low, and the stability of the rotating speed adjustment is poor. Therefore, the present embodiment realizes the control of the bus voltage by the closed-loop control of the motor rotation speed. As shown in fig. 3, by collecting the three-phase current i of the permanent magnet synchronous motor 10_a、i_b、i_cAnd after performing park transformation and clark transformation, performing frequency estimation on the transformed values to obtain an actual frequency f of the permanent magnet synchronous motor 10, and then using the actual frequency f and a target frequency f^*The difference value is subjected to V/f closed loop control to obtain the bus regulating voltageFinally, the voltage is regulated according to the busVoltage-current double loop control is performed to obtain the waveform of the pulse modulation signal PWM loaded to the two first switching devices T1, T2.

Specifically, a control block diagram of the dc bus voltage is shown in fig. 4. Firstly, the actual frequency f of the motor is obtained after frequency estimation. Then, the target frequency f is calculated^*Difference value with actual frequency f, proportional integral operation is carried out on the difference value to obtain bus calculation voltage Us, and finally, calculation is carried out according to the busCalculating the voltage Us and a preset adjusting parameter k to obtain the bus adjusting voltage

In particular, the bus regulates the voltage

The calculation of (c) can be implemented using the following formula:

in the formula 1, f^*And f is the target frequency of the motor and the actual frequency of motor operation, k, respectively_p、k_iAnd s is a parameter of the proportional integral calculation. As can be seen from equation 1, the bus regulates the voltage

Is the product of the bus calculation voltage Us and a preset regulation parameter k.

In order to stably operate the permanent magnet synchronous motor 10, the output voltage value of the bus voltage of the dc chopper circuit 11 must be adjusted according to the frequency command while the adjustment of the operating frequency of the motor is completed, so that the operating frequency of the motor needs to be controlled by controlling the on-time of the two first switching devices T1 and T2 in the dc chopper circuit 11. Control block diagram of two first switching devices T1 and T2 is shown in FIG. 5, and the regulated voltage of the bus is obtainedThereafter, the application obtains the bus regulation voltageActual voltage U to bus_dcPerforming a first proportional integral calculation, specifically, calculating the bus regulation voltage

Actual voltage U to bus_dcIs scaled by the differenceIntegral calculation to obtain a target current i^* _L. Then, the target current i is applied^* _LAnd the actual current i_LPerforming a second proportional-integral calculation to obtain a modulation voltage u_t. Wherein the actual current i_LIs the current of the inductor L1 on the dc chopper circuit 11. Calculating to obtain a modulation voltage u_tThen, the modulation voltage u is adjusted_tThe modulation is performed to obtain the waveform of the pulse modulation signal PWM, and the pulse modulation signal PWM is loaded on the two first switching devices T1, T2.

It can be seen that the present embodiment adjusts the bus voltage of the dc chopper circuit 11 by changing the pulse modulation signals PWM applied to the two first switching devices T1, T2, that is, by changing the on-time of the two first switching devices T1, T2. Wherein, the actual voltage U of the bus_dcI.e. the voltage across the capacitor C1, the actual bus voltage U_dcAnd is also the voltage applied across inverter circuit 12. When the actual bus voltage U_dcAfter being adjusted, the voltage across the inverter circuit 12 is synchronously adjusted, and therefore, the rotation speed of the permanent magnet synchronous motor 10 is adjusted, thereby realizing the frequency adjustment of the permanent magnet synchronous motor 10.

In this embodiment, the control of the six second switching devices of the inverter circuit 12 is performed by using a six-step control signal. Because the voltage utilization rate of the inverter circuit is not high when the inverter circuit modulates according to the SVPWM linear region, in order to expand the speed regulation range of the permanent magnet synchronous motor 10 and improve the utilization rate of the bus voltage, a six-step control signal mode is adopted for modulation and control. Specifically, referring to FIG. 3, at the acquisition target frequency f^*Then according to the target frequency f^*Calculating to obtain a corresponding target phase angle omega^*And using the target phase angle omega^*Six-step signal modulation is performed.

In this embodiment, in one cycle of the output frequency of the variable frequency control apparatus, the conduction phase angles of each of the second switching devices T3, T4, T5, T6, T8, and T8 are all 180 °, so that 6 basic voltage vectors (except for the zero vector) are respectively rotated by 60 ° to be switched, and the output waveforms of the corresponding phase voltage and line voltage are obtained as shown in fig. 6.

For example, one cycle of the output frequency of the variable frequency control device is divided into six stages on average, and each stage corresponds to a phase angle of 60 °. For each of the stages, three-digit numerical expressions are used for the control modes of the six second switching devices, for example, the control modes of the six stages are respectively "100", "110", "010", "011", "001" and "101". The first number from left to right indicates the on/off states of the two second switching devices T3, T4 of the first bridge leg, the second number indicates the on/off states of the two second switching devices T5, T6 of the second bridge leg, and the third number indicates the on/off states of the two second switching devices T7, T8 of the third bridge leg. In addition, a numeral "1" indicates that the switching device of the upper arm is on and the switching device of the lower arm is off, and a numeral "0" indicates that the switching device of the upper arm is off and the switching device of the lower arm is on, among the two second switching devices.

In the first stage, the control mode of the three bridge arms is "100", that is, the on-off states of the two second switching devices T3 and T4 of the first bridge arm are "1", that is, the second switching device T3 is turned on, and the second switching device T4 is turned off; the on-off states of the two second switching devices T5 and T6 of the second bridge arm are "0", that is, the second switching device T5 is turned off, and the second switching device T6 is turned on; the on-off states of the two second switching devices T7 and T8 of the third leg are "0", that is, the second switching device T7 is turned off, and the second switching device T8 is turned on.

In the second stage, the control mode of the three bridge arms is 110, that is, the on-off states of the two second switching devices T3 and T4 of the first bridge arm are 1, that is, the second switching device T3 is turned on, and the second switching device T4 is turned off; the on-off states of the two second switching devices T5 and T6 of the second bridge arm are "1", that is, the second switching device T5 is turned on, and the second switching device T6 is turned off; the on-off states of the two second switching devices T7 and T8 of the third leg are "0", that is, the second switching device T7 is turned off, the second switching device T8 is turned on, and so on.

Best of FIG. 6The upper waveform diagram is the phase voltage U of the phase a coil_a0The middle waveform diagram is the phase voltage U of the phase-b coil_b0The lowest waveform diagram is the line voltage U of the phase a coil and the phase b coil_abThe waveform of (2).

Due to the line voltage U_abIs an even function, and the line voltage U can be obtained according to Fourier analysis_abThe method comprises the following steps:

in formula 2, U_dcIs the actual voltage of the bus. According to equation 2, the preset tuning parameters in equation 1 can be obtained

It can be seen that, by applying the control method of this embodiment to control the ultra-high speed permanent magnet synchronous motor, the frequency of the permanent magnet synchronous motor is controlled by adjusting the bus voltage by the dc chopper circuit 11, the amplitude of the permanent magnet synchronous motor is controlled by the inverter circuit 12, and the control of the bus voltage is realized by adopting the single closed loop control of the frequency. Compared with the traditional motor control method, the frequency conversion control device adopted by the embodiment is additionally provided with the direct current chopper circuit, but because each second switching element of the inverter circuit does not need to be loaded with a control signal with extremely high switching frequency, the second switching element is protected, the control cost of the motor is reduced, and the harmonic content generated by the frequency conversion control device is reduced. In addition, the control method of the embodiment is simple, the program executed by the processor is not complex, the execution time of the processor is shortened, and the response speed of frequency adjustment is improved.

In addition, the frequency conversion control method and the frequency conversion control device of the invention can be applied to the control of ultra-high speed permanent magnet synchronous motors and the control of all high-frequency inversion systems, namely, the controlled frequency conversion equipment of the frequency conversion control method can be other frequency conversion equipment besides the ultra-high speed permanent magnet synchronous motors.

Finally, it should be emphasized that the present invention is not limited to the above-mentioned embodiments, such as the change of specific values of the parameters in the above formula 1, and the like, and such changes should be included in the protection scope of the claims of the present invention.