JPS6077689A - Regenerative power discharge circuit for motor drive inverter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a regenerative power discharge circuit used in an inverter for driving an induction motor.

Conventional configuration and its problems Traditionally, when an induction motor (hereinafter referred to as a motor) is operated using an induction motor inverter (hereinafter referred to as an inverter),
It is well known that when the frequency setting is rapidly lowered, the inertia of the motor and its load causes the motor to operate as a generator and return that inertial energy to the inverter, resulting in a so-called regenerative braking mode. The inverter absorbs this energy with the converter's smoothing capacitor, but as the capacitor voltage increases, there is a risk that the power transistor or capacitor may be destroyed due to overvoltage resistance. Therefore, ■ If the capacitor voltage exceeds the specified value, the inverter operation is stopped, the motor changes from regenerative braking mode to free run mode, and the so-called regenerative overvoltage cutoff operation is performed to protect the control circuit. The system detects this and stops the frequency drop until the regenerative voltage decreases to prevent the operation from stopping (stalling).When the regenerative energy decreases, the frequency decreases again and deceleration continues. built-in protection functions into the inverter,
For applications intended for braking, a large discharge resistor with c wattage? : By configuring a discharge circuit using i, an accessory device called a brake unit can be added that absorbs inertial energy during regeneration, or ■ reverse conduction can be made in the convergence section to regenerate it to the power supply side. The method of controlling regenerative energy is well known. However, as a user's request, it is desirable to prevent the above protection function ① from working as much as possible. Also,■
An intermediate, small, inexpensive, and simple regenerative energy control device is desired, such as the braking circuit shown in (2), which has an excellent function as an energy absorption device, but is large in size and does not require equipment that increases costs. It was rare.

Figure 1 shows the basic configuration of a conventional inverter with an attached device called a brake unit. 1 is a power supply;
The rectifier diode 3 constituting the 2-digit forward converter is a smoothing capacitor, and a discharge resistor 4 and a transistor 5 for driving it are connected to this capacitor 3 in an 8p column.

6 is an inverter section, and 7 is a motor.

In the above configuration, when the capacitor 1 becomes equal to or higher than the specified voltage, the transistor 5 turns on and the regenerated energy is consumed by the discharge resistor 4 c4, suppressing the upper row of the capacitor voltage, and increasing the voltage I am trying to prevent it from working (hereinafter referred to as Trinobu). but,
If the inertial energy is large, a resistor with a small capacity will lead to burnout, so a resistor with a large capacity must be used, and a forced cooling fan must be added to dissipate the heat generated. However, the disadvantages are that the volume of the inverter becomes large and the price becomes high. -Also, as a method to remove the capacitance of the resistor, it has a built-in thermal protector, and when the resistor reaches a specified temperature rise, it is turned on.
The safety of the regenerative power discharge section was ensured by a timer circuit that matched the temperature rise time constant of the resistor without burning out the resistor or deteriorating its characteristics. However, if the driving transistor 5 fails in the normal mode, the resistor may be burnt out,
This has the drawback of creating a dangerous situation in which an abnormality of 4.9% in impark voltage decreases.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a small, inexpensive, and safe discharge circuit.

This type uses a single star element or a combination circuit of a positive temperature coefficient thermistor and a resistor, and the self-switching action of the positive coefficient thermistor eliminates the need for extra protection functions such as a thermal protector or timer circuit.

DESCRIPTION OF EMBODIMENTS An example of the present invention will now be described with reference to the accompanying drawings. Figure 2 shows various characteristics of the positive temperature coefficient thermistor used in the present invention.
The resistance value is almost constant up to a certain temperature (
It has static characteristics (Figure 2b) that are stable (R = constant range), and the resistance value rises rapidly above this (Figure 2B), and its dynamic characteristics (Figure 2C) It is common for the thermistor to have a self-switching function that allows current to flow until it reaches the sudden change point of the resistance (called Curie point CP or switching temperature Ts, hereinafter abbreviated as Ts) due to self-heating of the thermistor, and then limits the current after a few seconds. Known and sown. The present invention utilizes the dynamic locking property of the above-mentioned positive temperature coefficient thermistor to improve the conventional drawbacks.

FIG. 3 shows an example of a circuit configuration in which the resistive element 4 shown in FIG. 1 is replaced with a positive q'I thermistor. In addition,
The preconditions for the configuration of this circuit are: - The inverter has a regenerative overvoltage and a built-in ζ/cut function.

■Maximum use of positive temperature coefficient thermistors? 1nIfkj:, J-
The regenerative overvoltage is greater than the specified value.

need to be satisfied. (2L) in FIG. 3 is an example of a single positive temperature coefficient thermistor PTC, and (b) is an example of a positive coefficient thermistor p'rc to increase the energy absorption capacity.

and PTC,2 are connected in parallel, (C) is an example in which the energy absorption capacity is reduced but the energy absorption time is lengthened by limiting the current flowing through the positive temperature coefficient thermistor PTC, (d) )&:I: (bl and (
An example of the configuration of the combination C) is 1, +1♂ζ configuration, 11 years old, 1.It depends on the application, such as the magnitude of regenerative energy and the frequency at which the regenerative mode occurs, but when using a commercially available positive temperature coefficient thermistor, (d ) is suitable.

Next, a specific example of the circuit configuration will be explained with reference to FIG.

Components that are the same as those shown in FIG. 1 are designated by the same numbers, and their explanations will be omitted. In the figure, 8 is an energy discharge section using a positive temperature coefficient thermistor shown in FIG.

9 is a power MO3 FET (corresponding to the power transistor 5 in FIG. 1). 10 is a regenerative overvoltage cutoff circuit.

Reference numeral 11 denotes a full-wave rectifier diode for protecting against incorrect wiring when a regenerative power discharge circuit is provided as an option. 12 operates at an appropriate specified voltage that is higher than the normal operating voltage and lower than the regenerative overvoltage operating voltage, and the power MO8-F
This is a regeneration mode detection circuit that operates ET9 ON-OFF.

Next, the operation will be explained. First, when the motor 7 is not in the regenerative state, the regenerative mode detection circuit 12 is inactive, so the power MO8-FET9 remains OFF, and the regenerative power discharge circuit is in the inactive state.

Next, when decreasing the frequency setting rapidly, etc., the motor 7
A case will be explained in which the system enters the regenerative state.

In the regenerative state, the capacitor 3 absorbs energy, so its voltage rises, and when it reaches the specified ON voltage of the regenerative mode detection circuit 12, the "war MO3-FET9
operates and consumes regenerative energy in the energy discharge section 8. As a result, when the capacitor voltage decreases and reaches the specified OFF voltage of the regeneration mode detection circuit 12, the power MO8
, Since the FET 9 is turned off, the energy consumption of the energy discharge section 8 stops, and the voltage of the capacitor 3 rises again. Through the repeated operation of the cycle, the regenerated energy is consumed in the energy discharge section 8, which helps in braking the motor 7. , suppress the voltage rise. When the regenerated energy is large, the regenerative state is long, or the regenerative state is repeated in a short period of time, use a positive characteristic thermistor P T C+
, PTC27: Operates to protect the positive temperature coefficient thermistor itself and the resistor R connected in series from burnout and characteristic deterioration by generating self-heat and suppressing energy consumption.

Of course, since the consumption of the energy discharge section 8 is reduced,
The voltage of capacitor 3 increases and regenerative overvoltage cutoff circuit 1
0 is activated and the output of the switching element of the inverter 6 is stopped and held, so that the regeneration of energy to the capacitor 3 is stopped. Furthermore, even if a switching element such as the power MO3-FET9 fails in a short-circuit mode, the regenerative energy cannot be discharged due to the self-switching action of the positive temperature coefficient thermistor, but there is no effect on the inverter circuit, so it is safe.

As described in detail, according to the present invention, there is no need to install a discharge resistor due to the self-switching action of the positive temperature coefficient thermistor, so extra protective functions such as conventional thermal protectors and timer circuits are unnecessary. becomes. Depending on the application, an optimal regenerative discharge circuit can be configured by selecting all combinations of positive temperature coefficient thermistors. Furthermore, safety is ensured against short-circuit mode failures of the switching elements that drive the energy discharge section. It has excellent effects such as being compact, small, and inexpensive.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the basic configuration of a conventional inverter including a regenerative power discharge circuit, Figure 2 is a characteristic diagram showing the basic characteristics of a positive temperature coefficient thermistor, and Figure 3 is a configuration example of the discharge circuit of the present invention. Circuit Diagram FIG. 4 is a circuit diagram according to an embodiment of the present invention. 3... Capacitor, 7... Electric motor, 8...
- Energy discharge section, 9... switching element, 12
...Regeneration mode detection circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 ♂-4'CI Mill lagv 1derAl(Jecn Figure 3 (α' Cb) (C1(/) Figure 4

Claims (1)

[Claims] When the motor enters a regenerative state, an energy discharge section including a positive temperature coefficient thermistor element connected in parallel to a capacitor that absorbs regenerative power and a switching element that drives this energy discharge section generate a voltage higher than that during normal operation. A regenerative power discharging circuit for an inverter for driving a motor, comprising a regenerative mode detection circuit that operates the switching element at a specified voltage lower than a regenerative overvoltage operating voltage.