JP2553504B2 - Brushless DC motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor which detects a counter electromotive voltage generated in a stator winding and omits a rotor position detecting sensor.

2. Description of the Related Art In recent years, brushless DC motors are being used in various fields because of their high efficiency and easy control of rotation speed. However, when it is used as a compressor for refrigeration equipment, it is difficult to use it because there is a sensor for detecting the rotor position. However, various methods of detecting the position of the rotor from the counter electromotive voltage of the stator winding have been proposed, and the sensor can be omitted, and the brushless DC motor can be used for compressors for refrigeration equipment.

Hereinafter, a brushless DC motor without such a sensor will be described with reference to the drawings.

Generally, such a DC brushless motor has a structure as shown in FIG. In FIG. 7, 1 is a DC power supply. 2 is a power circuit, which is a semiconductor switching element
It is composed of 3a to 3f. Reference numeral 4 is a stator winding, which is a three-phase Y connection, and each input is connected to the output of the power circuit 2. A rotor 5 has a permanent magnet.
A counter electromotive voltage detection circuit 6 detects the rotational position of the rotor 5. Reference numeral 7 denotes a starting circuit, which gives a starting pulse for accelerating to an operable rotational speed because the counter electromotive voltage detection circuit 6 cannot operate at the time of starting. A commutation circuit 8 converts a signal from the back electromotive voltage detection circuit 6 or the starting circuit 7 into a timing required to operate the semiconductor switching elements 3a to 3f. Reference numeral 9 is a drive circuit, which is a semiconductor switching element according to the timing from the commutation circuit 8.
Operate 3a to 3f.

The operation of the brushless DC motor configured as described above will be described below.

First, when the rotor 5 is stopped, a counter electromotive voltage is not generated in the stator winding 4, so that the counter electromotive voltage detection circuit 6 cannot detect the position. Therefore, a starting pulse is generated by the starting circuit 7, an appropriate voltage is applied, a current is passed through the stator winding 4 to rotate the rotor 5, and the frequency of the starting pulse is increased to accelerate. When rotated in this manner, a counter electromotive voltage is generated and the counter electromotive voltage detection circuit 6
The position can be detected by and the signal continues to rotate thereafter. Here, in order to apply a voltage to the stator winding 4, the semiconductor switching elements 3a, 3c, 3e are chopped at a high frequency with a certain duty (ON ratio). By changing the duty, it is possible to change the voltage applied to the stator winding 4 and the rotation speed of the rotor 5.

Next, the concrete circuits of the starting circuit 7 and the commutation circuit 8 are
It is shown in the figure and will be described below. 10 is a signal selection circuit
Is constituted by a D gate 10a~10f and OR gate 10G～10i, when switching signal CH is at the "H" level, each input X _1, Y _1, Z ₁ is output to the output X _3, Y _3, Z ₃ when the switching signal is "L" level output X _3, Y _3, each of the Z ₃ input X _2, Y _2, Z ₂ is adapted to be outputted. Reference numeral 11 is a logic processing circuit, which is composed of AND gates 11a to 11f and has the following logic.

_{A 1 '= X 3 · 3} , B 1' = Y 3 · 3, C 1 '= Z 3 · 3 A 2 = 3 · Y 3, B 2 = 3 · Z 3, C 2 = 3 · X 3 start The circuit 7 is the same as that shown in FIG. 7, and has a switching signal CH, starting pulses X ₂ , Y ₂ , Z ₂ and duty command data d as an output, and a start signal START as an input. Reference numeral 12 denotes a duty generating circuit, which produces a signal D having the duty according to the duty command data d obtained from the starting circuit 7. 13 is a chopping synthesis circuit AND
The signals A ₁ , B ₁ , C ₁ are produced by ANDing A ₁ ′, B ₁ ′, C ₁ ′ and D, which consist of gates 13a to 13c. Where the signals A ₁ ′, B ₁ ′,
C ₁ ′, A ₂ , B ₂ and C ₂ respectively operate the semiconductor switching elements 3a, 3c, 3e, 3b, 3d and 3f via the drive circuit 9.

FIG. 9 shows a flowchart of the conventional starting circuit 7 in the circuits shown in FIGS. 7 and 8. 14 is the initial setting and sets all outputs to "L". Start signal ST at 15
Having ART input, move to the next processing after input. At 16, the duty setting data is set to d and the duty is set to d ₀ %. The start pulse is given at 17-17 to 17-n below. In 17-1
Set only X ₂ and Z _{2 to} “H” and set Y ₂ to “L”. (Hereinafter, only those that are set to “H” are also described.) In this state, hold for time T ₁ . The same operation is repeated up to 17-n. 18
Then, the switching signal CH is set to "H", and at 19, the rotation of the rotor is continued by the output signals X ₁ , Y ₁ , Z ₁ of the counter electromotive voltage detection circuit 6.

The operation of the above flow chart is shown in the timing charts of FIGS. 5 and 6. That is, FIG. 5 shows the operation from 14 to 18 in FIG. 9, and FIG. 7 shows the operation at 19 in FIG. Timer time is generally T ₁ ≧ T ₂ ≧ T ₃ ≧ ...
It is set so that ≧ T _n-1 ≧ T _n, and the forward charge acceleration is performed.

FIG. 10 shows the operation of the brushless DC motor in the starting circuit configured as described above. The Figure 10 a to time t ₁ in relation to the motor applied voltage and time _{[= T 1 + T 2 + T} 3 + ...... + T n ] is the starting motor applied voltage [duty] Whenever
d ₀ %. After time t ₁ , the voltage applied to the motor is increased by another method. FIG. 10b shows the relationship between the frequency of the output signal A ₂ and time, which is determined by the starting pulse until time t ₁ and gradually rises as shown in the timing chart of FIG. After time t ₁ , the frequency is determined by the voltage applied to the motor at a, and therefore the frequency gradually increases as shown in the figure. Figure 10c
Indicates the motor current at this time, and a very large current flows until time t ₁ .

Problems to be Solved by the Invention However, in the above structure, a large current may flow at the time of starting as shown in FIG. 10c. The reason will be described with reference to FIG. FIG. 11a is a circuit of a general brush motor, and b is its equivalent circuit.

The following equation holds in the special circuit b Transform the above formula Is obtained. From this equation, when the rotation speed N is small, the motor current I _M also becomes large when the applied voltage E is large. Therefore, a large current flows at the time of starting. As described above, when a large current flows, not only a semiconductor switching element with a large capacity is required, but also the rotation of the rotor is severely pulsated and unstable.

In view of the above problems, the present invention provides a brushless DC motor that can reduce the motor current I _M at the time of starting and has stable and small pulsation of rotation of the rotor.

Means for Solving the Problems In order to solve the above problems, a brushless DC motor according to the present invention comprises a DC power supply, a power circuit formed by connecting six semiconductor switching elements in a three-phase bridge, and a three-phase power circuit. A connected stator winding, a rotor having a permanent magnet, and a counter electromotive voltage detection circuit that detects a counter electromotive voltage of the stator winding to detect its rotational position during rotation of the rotor. A switching circuit for switching the semiconductor switching elements of the power circuit by the output of the counter electromotive voltage detection circuit and a commutation circuit for starting the rotor based on a starting pulse; and a count value from a counting means at the time of starting the rotor. A signal generating means for generating a starting pulse of a predetermined frequency and a duty setting hand for outputting a predetermined duty setting value according to the frequency of the starting pulse according to the count value. A timer means for outputting the count value to the counting means at a predetermined time interval, and a duty corresponding to the output of the duty setting means in synchronization with an increase in the frequency of the start pulse of the signal generating means. It is characterized in that the three semiconductor switching elements on one arm of the power circuit are chopped, and when the frequency of the starting pulse of the signal generating means reaches a predetermined value, the operation is switched to the operation by the counter electromotive voltage detection circuit. .

The present invention has the above-described structure, thereby lowering the motor current by applying a low voltage to the stator winding at the time of a low frequency signal at the start of starting, and minimizing the pulsation of the rotation of the rotor for stable operation. You will get it.

Example A brushless DC motor according to an example of the present invention will be described below with reference to the drawings. 7th overall composition
The description is omitted because it is the same as in FIGS. FIG. 1 is a detailed circuit of the starting circuit 7. Reference numeral 7-a is a counting means, and the start signal START is input and the count output r is counted up by the input of CLOCK. The 7-b is a duty setting means counting means 7-a count value r, and outputs the duty set value d _r. 7-c is a signal generating means, which is a count value r of the counting means 7-a.
The signals X ₂ , Y ₂ and Z ₂ determined by are output. Reference numeral 7-d is a timer means, which outputs after a time _Tr from the moment when the count value of the counting means 7-a is counted up. The output of the timer means 7-d is the output of the counting means 7-a.
It is input to CLOCK and the output r of the counting means 7-a is counted up. The operation of the above structure will be described with reference to FIG. In the flow chart of FIG. 2, 20 is an initial setting, and all outputs are set to "L". At 21, the start signal START is input, and after the input, move to the next processing. 2
2-1 to 22-n give duty setting data and start pulse. In 17-1, the duty setting is d ₁
%, Set only X ₂ and Z _{2 to} “H”, and set Y ₂ to “L”. In this state, hold for time T ₁ . 17-n
Repeat until At 23, the switching signal CH is set to "H", and at 24, the rotation of the rotor is continued by the output signals X ₁ , Y ₁ , Z ₁ of the back electromotive force detection circuit 6.

The operation of the above flow chart is shown in the timing charts of FIGS. 5 and 6. Fig. 5 is from 20 of Fig. 2
The operation up to 23 is shown, and FIG. 6 shows the operation at 24 in FIG. The duty setting is generally d ₁ ≤d ₂ ≤d ₃ ≤ …… ≤d
Set so that _n-1 ≤ d _n, and the timer time is T ₁ ≥ T ₂ ≥ T ₃
Set so that ≧ …… ≧ T _n-1 ≧ T _n, and accelerate sequentially.

FIG. 3 shows the operation of the brushless DC motor in the starting circuit configured as described above. FIG. 3A shows the relationship between the voltage applied to the motor and the time, and the motor is started up to time t ₁ [T ₁ + T ₂ + T ₃ + ... + T _n ] and the motor applied voltage is changed according to the starting pulse frequency. After time t _1, the motor applied voltage is increased by another method. FIG. 3b shows the relationship between the output signal A ₂ frequency and time, which is determined by the start pulse until time t ₁ and gradually increases as shown in the timing chart of FIG. 5, and immediately before time t ₁ . The part where the frequency changes but the motor applied voltage is constant is provided. After time t ₁ , the frequency is determined by the voltage applied to the motor in FIG. FIG. 3c shows the motor current at this time, but the current decreases in the portion where the frequency rises and the motor applied voltage is constant just before time t ₁ .

Next, how to determine the duty set values d ₁ , d _2, ... D _n will be described with reference to FIG. FIG. 4a is a graph showing the rotation speed and load torque of the motor used, and the duty is taken as a parameter. Now, the rotational speed of the relationship between duty and parameter T _S When T _S required torque at startup graph in FIG. 4 b is obtained from the graph of Figure 4 a. Based on this graph, it is possible to find the optimum duty for the rotation speed at the time of starting. For example, it can be seen that the duties d _D and d _E are optimal when the engine speed at startup is n ₄ and n ₅ . However, since variations and power supply voltage fluctuations are not taken into consideration here, it is necessary to add a necessary margin to the duties d _D and d _E in actual operation. In this way, the duties d ₁ , d _{2 to} d _n are determined.

As described above, according to the present embodiment, at the same time that the starting pulse is output from the starting circuit at the time of starting, the motor current at the time of starting is reduced by applying the voltage according to the frequency of the starting pulse to the motor. Since the semiconductor switching element has a small capacity, and an appropriate voltage is applied to the motor, the pulsation of the rotation of the rotor is also small and stable operation is possible.

EFFECTS OF THE INVENTION As described above, the present invention is provided with the starting circuit that generates the starting pulse when starting the rotor and, at the same time, changes the voltage applied to the stator winding according to the frequency of the starting pulse. Thus, by applying a low voltage to the stator winding when a low frequency signal is generated at the time of starting, it is possible to reduce the motor current and also minimize the pulsation of the rotation of the rotor to obtain stable operation.

[Brief description of drawings]

FIG. 1 is a block diagram of a starting circuit of a brushless DC motor of the present invention, FIG. 2 is a flowchart of the starting circuit of the present invention,
3 a, b and c are characteristic diagrams of motor applied voltage and output signal frequency motor current with respect to time according to the present invention, and FIGS. 4 a and b are characteristic diagrams showing rotational speed with respect to load torque and rotational speed with respect to duty. Fig. 5 is a timing diagram at the time of starting, Fig. 6 is a timing diagram at the time of normal operation, Fig. 7 is an overall configuration diagram of the brushless DC motor, Fig. 8 is a circuit diagram of the commutation circuit and the starting circuit of Fig. 7, FIG. 9 is a flowchart of a conventional starting circuit, FIGS. 10 a, b and c are characteristic diagrams of motor applied voltage and output signal frequency motor current with respect to time by the conventional starting circuit, and FIGS. 11 a and b are DC motors. It is a basic block diagram and its special price circuit diagram. 1 ... DC power supply, 2 ... power section, 4 ... stator winding,
5 ... Rotor, 6 ... Counter electromotive voltage detection circuit, 7 ... Starting circuit, 8 ... Commutation circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Endo 3-22, Takaidahondori, Higashi-Osaka City, Matsushita Refrigerating Machinery Co., Ltd. (56) Reference JP-A-49-58311 (JP, A)

Claims (2)

(57) [Claims] 1. A DC power supply, a power circuit formed by connecting six semiconductor switching elements in a three-phase bridge, a stator winding connected in three phases, and a rotor having a permanent magnet.
A counter electromotive voltage detection circuit for detecting a counter electromotive voltage of the stator winding in order to detect a rotational position of the rotor during rotation, and a counter electromotive voltage detection circuit for switching a semiconductor switching element of the power circuit. A commutation circuit that is performed based on the starting pulse at the time of starting and a signal generating means that generates a starting pulse having a predetermined frequency according to the count value from the counting means at the time of starting the rotor,
Duty setting means for outputting a predetermined duty setting value according to the count value according to the frequency of the starting pulse; timer means for inputting the count value and outputting a signal to the counting means at a predetermined time interval; In synchronization with an increase in the frequency of the starting pulse of the signal generating means, the three semiconductor switching elements of the one side arm of the power circuit are chopped at a duty corresponding to the output of the duty setting means, and the starting pulse of the signal generating means is changed. A brushless DC motor, wherein when the frequency reaches a predetermined value, the operation is switched to the operation by the back electromotive force detection circuit. 2. The brushless according to claim 1, further comprising a region where the frequency changes but the duty does not change after the start and immediately before switching to the operation by the back electromotive voltage detection circuit. DC motor.