JPS6129237B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor speed control circuit driven by a bridge type inverter using transistors.

Generally, a motor speed control circuit is often driven by an inverter composed of semiconductor switching elements. A thyristor is used as a semiconductor element, but in the case of a relatively small capacity motor, the first
It is possible to use a transistor type inverter as shown in the figure. In FIG. 1, 1 is a driving power source, 2-a, 2-b and 2-c are armature coils, 3-a, 3-b and 3-c are transistors corresponding to the so-called upper arm of the bridge, and 4-
A, 4-b and 4-c are transistors corresponding to the so-called lower arm. Common end of lower arm 1
A common terminal 7 is connected to a reference potential of a control circuit that controls each arm, and corresponds to a ground terminal in many cases. On the other hand, the upper arm is connected to the positive potential side of the drive power source 1. Further, 7-a, 7-b and 7-c are transistors that drive the upper arm;
-a, 5-b and 5-c are on the upper arm, and 6
-a, 6-b and 6-c are diodes connected in antiparallel to the lower arm. In such a bridge configuration, the input terminals 13-a, 1 of each arm
A commutation signal of a cyclic inverter as shown in FIG. 2 is applied to 3-b, 13-c, 14-a, 14-b and 14-c to drive a rotor (not shown).

Various methods can be considered to control the speed of this type of motor, but one method that achieves not only speed control but also high efficiency is to first turn on and off the transistors using a predetermined high-frequency pulse width signal. An application was filed regarding the method of operation (Special Application
49-100903). That is, by superimposing a pulse width signal with a sufficiently higher frequency on the commutation signal of the inverter shown in Fig. 2, and changing the on/off ratio to change the average voltage applied to the motor, This is for speed control.

As described above, the present invention provides more efficient operating conditions in a motor that is configured with a transistor bridge, and controls the speed of the rotor by turning on and off the transistors in a predetermined commutation state at a higher frequency. The purpose is to

Before describing the specific configuration of the present invention, the first
Using the inverter circuit shown in the figure, operating conditions when transistors are turned on and off using a high-frequency pulse width signal will be explained. As shown in FIG. 3, the transistor 3-a in the upper arm and the transistor 4-b in the lower arm are energized by the commutation signal, and a loop of currents i ₀ , i ₁ ′, i ₁ ″ as shown by the broken line arrows is generated. Consider the case where the armature current is supplied to the armature coils 2-a and 2-b through the above steps.Now, the high-frequency pulse width signal is used to control the transistors 3-a and 4-b to turn off at the same time. When this happens, armature coils 2-a and 2-
Due to the energy stored in the inductance of b, current i _a tries to continue flowing through the loop of current i ₂ ' and current i ₂ ''. This current flows into the drive power source 1 in the opposite direction. , which often has an undesirable effect on the power supply.To prevent this, a high frequency pulse width signal may be applied only to either the upper arm or the lower arm.
That is, when only transistor 3-a is off, current i _a flows in a closed loop of current i ₁ '' and current i ₂ ', and when only transistor 4-b is off, current i _a flows as current i ₂ ″ and current i ₁ ′ continue in a closed loop, and the drive power source 1 is not adversely affected. Furthermore, the method of applying a high frequency pulse width signal to only either the upper arm or the lower arm is advantageous in that the number of transistors that can operate at high frequencies can be reduced to half of the total. In that sense, it can be said that the operating conditions of the upper arm and lower arm are equivalent regarding the high frequency pulse width signal.

However, when the purpose is to actually perform highly efficient control, the method of applying high-frequency pulses to the upper arm and the method of applying high-frequency pulses to the lower arm are not equivalent. The present invention focuses on this point. That is, the basic principle of the present invention is to apply a high frequency pulse width signal only to the upper arm that is not connected to the common end with the control circuit of the inverter. By doing so, the following advantages can be specifically obtained.

(1) It is possible to reduce the internal loss of transistors based on high frequency operation.

(2) Controlling the upper arm transistor, which generally requires troublesome circuit processing, becomes relatively easy.

(3) Current interruption in the event of overcurrent is possible independently of the above-mentioned high-frequency operation using the transistor in the lower arm, which is easy to control.

Among these advantages of the present invention, especially (1) and
(2) will be explained in detail below with reference to FIGS. 4 and 5.

First of all, Fig. 4 shows each transistor 4 in the lower arm.
A circuit is shown in which negative bias is applied to the base sides of a, 4-b and 4-c by resistors 9-a, 9-b and 9-c and a bias power supply 10, respectively.
Generally, it is well known that the base of an on-off transistor is always kept at a negative bias in order to completely cut off the transistor. However, in the case of the application of the present invention, the addition of this negative bias has an extremely important meaning in reducing the junction capacitance of the transistor at cut-off rather than the cut-off characteristic of the transistor. The reason for this will be explained below. FIG. 5 shows a further simplified version of the state already shown in FIG. That is, since the lower arm transistor 4-b remains on, it is shown short-circuited, and the upper arm transistor 3-a is shown as a simple switch 15-a. Further, the lower arm transistor 4-a is shown approximately replaced with a transistor 12-a and a transistor junction capacitance 11-a.

Now, when the switch 15-a is off, the current i _a shown by the solid line is flowing, and the transistor 12-a is flowing.
The emitter-collector potential of -a is almost zero, and there is no charge in the transistor junction capacitance 11-a. Next, at the moment the switch 15-a closes, a current i _c for charging the transistor junction capacitance 11-a to the voltage of the drive power source 1 rapidly flows as shown in the figure. An instantaneous current flows into the base of the transistor 12-a through this transistor junction capacitance 11-a, and a collector current i _c ' amplified by the current amplification rate of the transistor 12-a flows. i
Although the section through which _c ' flows is generally short, the magnitude of current i _c ' is a large value due to the current short-circuited between switch 15-a and transistor 12-a.
The instantaneous power consumption in transistor 5-a and transistor 12-a becomes very large. The current i _c ' not only has an adverse effect on the drive power supply 1 itself, but also has a negative effect on the switch 1.
5-a, that is, the transistor 3-a, generates a large loss equal to the value of the collector current i _c ' multiplied by the internal potential drop of the transistor 3-a. Generally, the capacity of a power transistor is quite large, and as a result of this loss that repeatedly occurs at high frequencies, the overall efficiency of the motor decreases and the temperature of the transistor itself increases, which cannot be ignored. To eliminate this loss,
The bias power supply 10 shown in FIG. 4 provides a great effect. That is, by applying a negative bias to the base of the transistor 12-a, the current i _c flowing through the transistor junction capacitance 11-a does not flow to the base of the transistor 12-a, but is absorbed by the bias power supply 10. transistor 1
2-a is not conductive, and the collector current i _c ' mentioned above does not flow. Regarding the negative bias of the transistors in the lower arm, since the emitters of all the transistors in the lower arm are common and also common to the control circuit, it is possible to apply a common negative bias to the three transistors in the lower arm using one bias power supply. I can do it.

If the high frequency intermittent operation is performed by the transistors in the lower arm, it is necessary to take measures to bring the transistors in the upper arm into a negative bias state. However, since the emitter potential of the transistor in the upper arm varies depending on whether the transistor in the other arm is turned on or off, it is necessary to provide three negative bias power supplies for each of the three transistors in the upper arm. is extremely difficult, and in that sense, the method of operating the upper arm at high frequency is of great significance.

Next, replace the upper arm transistor with NPN
An example in which the device is constructed using only transistors will be explained with reference to FIG.

Figure 6 shows upper arm transistors 3-a to 3.
-c is driven by transformers 16-a to 16-b such as pulse transformers. In the circuit shown in FIG. 1, the upper arm transistor is a combination of a PNP transistor and an NPN transistor. This is to avoid troublesome problems in circuit processing, such as the need for a high-potential bias power supply when implementing an NPN Darlington circuit, for example. However, PNP transistors are expensive among general silicon power transistors, and NPN transistors should be used as much as possible. FIG. 6 makes this possible by using an inexpensive transformer.
That is, this is possible on the premise that the upper arm transistor always operates with a high frequency signal. Generally, a power transistor has a long turn-off time, and when the on/off pulse width ratio of a high frequency signal is increased to a certain level, the output becomes almost DC. In other words, the design condition that the device is always driven by a high frequency signal is possible, and it becomes possible to use an element that cannot pass a DC signal, such as a transformer. This point is also an advantage that can only be obtained when a high frequency is applied to the upper arm transistor.

As described above, according to the present invention, highly efficient and highly stable motor speed control is possible, which is highly effective industrially.

[Brief explanation of the drawing]

FIG. 1 shows an example of the configuration of a brushless motor control circuit that is the object of the present invention, FIGS. 2, 3, and 5 show its operation, and FIGS. FIG.

Claims (1)

[Claims] 1 armature winding with neutral point ungrounded Y-wired, 3
an inverter consisting of an upper arm having three transistors connected to the positive potential side of the drive power source and a lower arm having three transistors connected to the negative potential side; and a transistor controlling the on/off of the six transistors. a control circuit, the motor speed control circuit having a common terminal where the negative potential side is connected to a ground terminal of the control circuit of the transistor, comprising one bias power supply connected to the common terminal, and controlling the transistor. A motor speed control circuit characterized in that the circuit controls on/off the commutation signal of the upper arm of the inverter using a pulse width signal having a higher frequency than the frequency of the commutation signal of the lower arm of the inverter.