JPH0824434B2 - Speed control method of brushless DC motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control method for a brushless DC motor, and more particularly to a brushless DC motor of a system that measures a rotation cycle from a position detection signal to calculate a rotation speed. It relates to a speed control method.

[Background of the Invention]

A conventional speed control method of this type is, as described in Japanese Patent Laid-Open No. 59-44991, measures the time for each electrical angle of 60 degrees from a position detection signal, and sets n ₁ as a positive integer for electrical angle of 60 n ₁ degrees. Calculation of time, calculation of rotation speed from that time, deviation of detection rotation speed and command rotation speed which is the calculation result Proportion of rotation speed, integration, calculation of differential term, and based on this, output voltage or output current of inverter It was done through the five processing steps of decision.
However, the first process, that is, the measurement of the time for each electrical angle of 60 degrees and the other processes following it were asynchronous. That is, there is a problem that after the time of 60 degrees is calculated, there is a time delay from the calculation result to the determination of the inverter output voltage, which causes a decrease in the response speed of the speed control system.

In particular, when a brushless DC motor adopting a conventional speed control method is used as a compressor motor, the following problems occur. That is, a compressor used in a room air conditioner or a refrigerator generally has a structure in which a driving motor is hermetically sealed in a chamber, and a load torque applied to the motor of the compressor is equal to that of a rotary compressor or a reciprocating compressor. Regardless of which one, there is a large pulsation with respect to the rotation angle, and the maximum load torque reaches approximately three times the average load torque. Then, this pulsating load has a pattern that is approximately determined with respect to the rotation angle. Therefore, in the method of performing the speed control asynchronously with the position detection signal synchronized with the rotation angle like the conventional speed control, the output voltage of the inverter is promptly determined according to the load that changes according to the rotation angle. Becomes difficult. As a result, the torque difference between the motor output torque and the load torque increases, rotation pulsation occurs, the amplitude of the rotation pulsation increases, especially at low speeds, and the frequency of the rotation pulsation also decreases, so the vibration of the entire chamber becomes severe. There was a problem.

[Object of the Invention]

An object of the present invention is to solve the above problems in the conventional speed control method, and to provide a speed control method for a brushless DC motor capable of speed control in response to a high speed even when the load changes with respect to the rotational position. To provide.

[Outline of Invention]

A feature of the present invention is that a load that changes according to a rotation angle is driven by a permanent magnet rotor type synchronous motor, and the synchronous motor is driven by an inverter that converts DC into three-phase AC. A means for detecting the magnetic pole position of the rotor and outputting a position detection signal is provided, the rotation speed of the rotor is detected from the position detection signal, and the inverter speed of the inverter is determined according to the detected rotation speed and the commanded rotation speed. In speed control of a brushless DC motor of a method of determining an output voltage or an output current and performing speed control processing, a timing signal is generated for each 60 electrical degrees from the position detection signal, and n ₁ is an integer of 2 or more. The time for each electrical angle 60n ₁ degree is measured from the timing signal, and n ₂ is an integer smaller than n ₁ and is selected at a low speed during rotation to a number smaller than during high speed rotation, and the electrical angle is calculated for each 60n ₂ degree time. Measured in Calculates the rotation speed from between performs a process for determining an output voltage or output current of the inverter based on this, in which to carry out by synchronizing the speed control processing to said position detection signal.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a configuration diagram of a brushless DC motor to which the present invention is applied, the main circuit of which is configured to supply power from a DC power source 1 to a synchronous motor 3 via an inverter 2. Here, the magnetic pole position of the permanent magnet type rotor 4 of the synchronous motor 3 is detected by the position detection circuit 5 using the output voltage of the inverter 2, and from this position detection signal, the control circuit 6 causes the rotor 4 to rotate. The switching control signal is supplied to the transistor in the inverter 2 corresponding to the rotational position via the base driver 7.

FIG. 2 shows the operation of the brushless DC motor,
It is a signal waveform diagram of each part of the main circuit. 2A shows a position detection signal output from the position detection circuit 5, and FIG. 2B shows an electric angle 60.
The timing signal PS, (c) is a triangular wave carrier and has a constant oscillation frequency. FIG. 2 (d) is a modulation signal generated by the slice level D _{1 in} FIG. 2 (c), and the drive signal (e) of the transistor is changed by the logical processing with the position detection signal (a). Made Here, the rotation speed of the brushless DC motor is determined by changing the output voltage of the inverter 2 according to the slice level D ₁ .

FIG. 3 is a control system diagram according to the speed control method of the present embodiment,
These are realized by the configuration in the control circuit 6 in FIG. First, at I ₁ in FIG. 3, the electrical angle
The time T corresponding to one cycle is calculated by multiplying the time of two cycles (T _i + T _i-1 ) of the timing signal PS [60 (b) in FIG. 2] every 60 degrees, and _{In 2} , the rotation speed N is N = K /
Calculated by T (K is a constant), and in I ₃ , the deviation between the detected rotation speed N and the command rotation speed N _R is proportional, integral, and
The differential level K _P , K _I , K _D is obtained, and the slice level D ₁ is determined from the sum (K _P + K _I + K _D ). These processes are performed by the microcomputer in the control circuit 6 or the like. ,
It is performed in synchronization with the PS signal every 60 electrical hours.

FIG. 4 is a diagram showing a time relationship between the PS signal and the above processing. The processes I ₁ , I ₂ , and I ₃ are continuously performed at one time for each electrical angle of 60 degrees, while the information for calculating the rotational speed is I ₁
Each time the processing of (1) is executed, the time of an electrical angle of 120 degrees corresponding to two cycles of the latest PS signal is used.

According to the above method, by using two cycles of the PS signal as the information of the number of revolutions, the dispersion of the measurement values generated in each cycle is averaged, and the time measurement results of the two cycles are immediately measured at the slice level. Since it is reflected in D ₁ , there is an effect that the accuracy of the detected rotation speed is improved and the response of the speed control system accompanying a change in the rotation speed becomes faster.

Another embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a control system diagram showing the speed control method according to the present embodiment. The difference from the control system diagram shown in FIG. 3 is that
In II _1, switches the computation of one cycle time T between the time of high speeds and low speed, which has to switch II _1, II _2, even execution period II ₃ and subsequent processing, II _2, II ₃ The contents of the process are the same as in the case of FIG.

That is, since it takes a certain amount of time to execute a process related to speed control by a micro computer or the like, one cycle of the PS signal becomes short at high speed, and processing within this one cycle becomes difficult. In order to avoid this, in the high-speed rotation region, in the embodiment shown in FIGS. 5 and 6, each process relating to speed control is executed every three cycles of the PS signal, that is, every 180 electrical degrees. It was done like this. further,
In the high-speed rotation region, the variation of the component parts of the position detection circuit 5 relating to the position detection signal has a great influence on the variation of the cycle of the PS signal. Therefore, the processing of II ₁ is executed as the information of the rotation speed calculation. 6 of the latest PS signal each time
It is averaged using the time of the electrical angle of 360 degrees corresponding to the cycle.

FIG. 6 is a diagram showing the time relationship between the PS signal and the processes II ₁ , II ₂ , and II ₃ in the high-speed rotation region. Each process is continuously executed in synchronization with the PS signal at each electrical angle of 180 degrees, and the information for calculating the rotation speed is assumed to use the time for 6 cycles of the latest PS signal each time. There is.

Here, even if the three processes of II ₁ , II ₂ , and II ₃ are not continuously executed, the same effect can be obtained by dividing each process and executing each process in synchronization with the PS signal. To be

〔The invention's effect〕

According to the present invention, since the time for each electrical angle 60n ₁ degree of the position detection signal is used as the information of the number of revolutions, the variation in the measured value generated in each cycle is averaged and the speed control is performed for the position detection signal. Since the processing is performed synchronously, especially for driving a load that fluctuates according to the rotation angle,
The detection accuracy of the rotation speed is improved, and the change in the rotation speed caused by the load change can be promptly reflected in the processing of the output voltage and output current of the inverter. Therefore, the conventional speed control processing is executed regardless of the angle. A stable and high-speed control response can be achieved compared to the asynchronous method, and speed control of a brushless DC motor with less rotation pulsation can be realized. Furthermore, according to the present invention, in the high-speed rotation region in which the change in the rotation speed caused by the change in the load is alleviated by the increase in the inertial force generated by the load and the motor, the processing time of the speed control system is taken into consideration in comparison with the case of the low speed. Since n ₂ is increased, it can be said that the control method has excellent practical effects.

[Brief description of drawings]

FIG. 1 is a block diagram of a brushless DC motor to which the present invention is applied, FIG. 2 is a signal waveform diagram of each part showing the operation of the motor in FIG. 1, and FIG. 3 is a speed control method according to an embodiment of the present invention. 4 is a control system diagram showing the speed control process execution timing of FIG. 3, FIG. 5 is a control system diagram showing a speed control method according to another embodiment of the present invention, and FIG. FIG. 5 is a diagram showing a process execution timing of speed control of FIG. 5. 1 ... DC power supply, 2 ... Inverter, 3 ... Synchronous motor, 4 ... Rotor, 5 ... Position detection circuit, 6 ... Control circuit, 7 ... Base driver, PS ... Timing signal, T
…… 1 cycle time, T _{1 to} T ₆ …… Timing signal PS
Time every 60 degrees, N …… rotation speed, N _R …… commanded rotation speed, D ₁ …
… Slice level.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumio Tajima 4026 Kujicho, Hitachi City, Ibaraki Prefecture, Hitachi Research Institute, Ltd. In Tochigi Plant (56) References JP 59-136088 (JP, A) JP 60-167695 (JP, A)

Claims (1)

[Claims] 1. A load, which varies depending on a rotation angle, is driven by a permanent magnet rotor type synchronous motor, and the synchronous motor is driven by an inverter for converting DC into three-phase AC. A means for detecting the magnetic pole position of the child and outputting a position detection signal is provided, the rotational speed of the rotor is detected from the position detection signal, and the output of the inverter is output according to the detected rotational speed and its commanded rotational speed. In a speed control of a brushless DC motor of a method of determining a voltage or an output current and performing a speed control process, a timing signal is generated for each electrical angle of 60 degrees from the position detection signal, and n ₁ is an integer of 2 or more, and the timing is set. Measure the time for each electrical angle of 60n ₁ degree from the signal, select n ₂ as an integer smaller than n ₁ , and select a number smaller than that during high-speed rotation at low speed rotation and set the above for each electrical angle 60n ₂ degree time. Measured time The brushless DC motor is characterized in that the number of revolutions is calculated from the above, a process for determining the output voltage or the output current of the inverter is performed based on this, and the speed control process is performed in synchronization with the position detection signal. Speed control method.