JPS6225885A - Inverter regenerative braking control device - Google Patents

Abstract

PURPOSE:To protect an apparatus sufficiently when regenerative energy increases by ON-OFF duty controlling the conduction of a resistor for absorbing power at a time when conditions in which regenerative energy must be absorbed are satisfied. CONSTITUTION:Voltage VD on the DC side of an inversion section rises when an induction motor is brought to the state of generation, and a signal is transmitted over a switching control circuit 4 from a comparator OP when the voltage VD reaches reference voltage or more. The switching control circuit 4 receives an output from the comparator OP, decides the turn-ON of a switching element TR and generates an ON signal. A conduction time detecting circuit 5 counts the ON signal, and detects the time when the switching element TR is conducted. A period control circuit 6 belongs to a kind of a timer circuit, and clears the conduction time detecting circuit at every predetermined fixed period.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an inverter that is equipped with a power absorption resistor on the DC side of the voltage source inverter to enable regenerative braking.
In particular, the present invention relates to a regenerative braking control device for an inverter that suppresses the temperature rise of a power absorbing resistor with a simple configuration.

[Background of the invention]

Machine tools that require variable speed drive often use induction motors that are variable speed controlled by an inverter. Regenerative braking control, which applies braking by absorbing the electrical energy generated by the vehicle, has been known for some time.

Figure 6 shows a conventional example of one device on the regenerative braking side of such a voltage source inverter, where 1 is a forward conversion section IA.
, an inverse conversion unit IB, a voltage source inverter consisting of a capacitor IC, 2 a regeneration control unit consisting of a comparator OP, R a resistor for absorbing regenerative power, TR a switching element such as a transistor, and 1M an induction motor. be.

Comparator OP consists of an operational amplifier, and voltage source inverter 1
The DC side voltage VD is taken in, and when it becomes higher than a predetermined reference voltage V, the switching element TR is turned on, thereby causing the resistor R to consume the energy generated by the induction motor IM, and applying braking. do.

Note that such regenerative braking control devices are disclosed in, for example, Japanese Utility Model Application No. 49-67119 and Japanese Utility Model Application No. 49-7370.
This is disclosed in Publication No. 9 or Japanese Utility Model Application Publication No. 49-119710.

By the way, in such a conventional device, the voltage v on the DC side
When Il becomes equal to or higher than the reference voltage 71, the switching element TR is turned on unconditionally.
If the regenerated energy by the induction motor IM is large, power will continue to be consumed by the resistor R for a long time.

However, if there is sufficient margin in the rated power of the power absorbing resistor R, there will be no particular problem, but due to cost reasons, it is not recommended to use such a large capacity resistor for -S. Therefore, in conventional devices, when the regenerated energy becomes large, the resistor R becomes significantly overheated, which may lead to equipment failure.

Further, at this time, there is also a problem that the temperature of the switching element TR increases significantly.

Therefore, in conventional devices, the temperature of the resistor R and the switching element is detected, and when the temperature exceeds the temperature, the switching element TR is prohibited from conducting, or a thermal time relay is inserted in series with the resistor R. When the current continues to flow for a predetermined period of time or more, the switching element TR is kept off.

However, for this reason, conventional devices require a power absorption resistor, a means to detect the temperature of the switching element, a timed relay, etc., which tends to increase costs, and furthermore requires a reset operation after the switching element is turned off. This has the disadvantage that the operation is likely to be complicated.

[Purpose of the invention]

The object of the present invention is to eliminate the drawbacks of the prior art described above, and to eliminate the need for temperature detection means, thermal time relays, etc.
The regenerative braking side of a voltage source inverter that provides sufficient protection for equipment when regenerative energy becomes large?
l equipment is provided.

[Summary of the invention]

In order to achieve this object, the present invention is characterized in that the conduction of the power absorbing resistor is controlled on/off duty when the conditions for absorbing regenerative energy are satisfied.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A regenerative braking control device for a voltage source inverter according to the present invention will be described in detail below with reference to illustrated embodiments.

FIG. 1 shows an embodiment of the present invention. In the figure, 3 is a regeneration control circuit, 4 is a switching control circuit, 5 is a conduction time detection circuit, and 6 is a periodic control circuit, and the others are the conventional example shown in FIG. is the same as In addition, in this Figure 1, the capacitor IC
Only the inverter, induction motor IM, etc. are omitted.

The switching control circuit book is from Comparator OP (■.

Upon receiving a signal indicating that the regenerative braking condition (≧V, ) is satisfied, it determines whether to turn on the switching element TR and generates an on signal.

4 The appropriate time detection circuit 5 counts the above-mentioned ON signals, and the switching element TR reaches 21! It works to detect the passing time.

The period control circuit 6 is a type of timer circuit, and functions to generate a clear signal every predetermined constant period T.

Next, the operation of this embodiment will be explained.

When the induction motor aIM enters the power generation state, the voltage V on the DC side of the inverse converter IB rises, and as a result, when the voltage V becomes equal to or higher than the reference voltage 71, the output of the comparator OP is inverted, which causes the switching control circuit to 4 is given a signal.

When a signal is input from the comparator oP, the switching control circuit 4 reads the ON time (integrated value) TON of the switching element TR within the current control cycle period from the conduction time detection circuit 5, and calculates this value. The time TON and the preset upper limit value T of the on time. , compare with □. Note that the setting of this upper limit value TaNH□ will be described later.

As a result of comparison, time T. N is the upper limit T. When it is smaller than NMAX, a signal is output that turns on the switching element TR for a certain unit time t5. In this example, ta-50rnS is used. At the same time, the switching element TR to the conduction time detection circuit 5
It sends a signal that it has been turned on once.

This operation occurs when the DC voltage VD becomes smaller than the reference value v1, the output of the comparator OP is inverted again, or the integrated value T of the on-time of the switching element TR. H is the upper limit T. □1. This is repeated until the limit is exceeded. In other words, when the integrated values T and N of the on-times exceed the upper limit II ``r 0 □□, the signal that turns on the switching element TR is not output even if the switching element TR is originally turned on. .

On the other hand, the conduction time detection circuit 5 that performs the Mi calculation function of the on time has an internal counter, and the switching control circuit 4
When it receives a signal indicating that the switching element has been turned on, it increments this counter.

In this way, the integrated value T of the on-time of the switching element TR. H is a constant unit time t for the switching control circuit 4 to turn on the switching element TR;
can be obtained by multiplying by the count value N of the force 6 counter inside the conduction time detection circuit 5. However, since this count value N will eventually reach the upper limit value if it is simply integrated, it is reset every fixed time period T, and the setting of this fixed time period T will be described later. Note that this constant time T is the period vn
It is designed to be measured with mm times Ni6. That is, this circuit 6 has an internal timer function, which measures a certain period of time T, and outputs a signal for resetting the internal counter of the conduction time control circuit 5 every time T.

Therefore, the above operation is shown in a time chart as shown in Fig. 2. As a result, according to this embodiment, by appropriately giving the above-mentioned values T, □□ and time T, regenerative braking power absorption can be achieved. This makes it possible to make maximum use of the capabilities of the resistor R and switching element TR, and to control their temperatures to keep them below the allowable value.
Setting of this upper limit value TONNAI+ and time T will be explained.

First, when the operation pattern of the regenerative braking device is already determined, it is easiest to set the time T to the time corresponding to one cycle of the operation pattern.

On the other hand, if the pattern is unknown for a general-purpose product, a simulated pattern that is considered to be the most common may be assumed and set at the time of one cycle of the simulated pattern.

In the embodiment of the present invention, the upper limit T was set to 2 minutes.

This is based on JEM standard 1022.

Next, the upper limit value T of the on-time of the switching element and the set of □□ may be determined as follows.

Generally, the temperature rise and fall of a heating element is expressed by the following equation in the case of repeated loads (see figure).

θ1==(θ,゛−θm)(1e ”) −・
−(1) θ is 20, e Shiyuki −・−・・−・−−
−1−・−・−・−・・・−・・−(2) θ,・・・・
Maximum value of temperature rise during control θ, '... Maximum value of temperature rise during continuous load θ8... Minimum value of temperature rise during control τ, ... Thermal time constant of temperature rise t, ... Time during which power is consumed τ3 ... Thermal time constant of temperature drop tt ... Time during which power is not consumed In the above equation, θ, ゛, τ1. τ2 is the element used in the regenerative braking device and the maximum value θ of temperature rise during zero-order control, which is calculated or actually measured from the cooling conditions, and the power absorption resistor R or switching element TR of the regenerative braking device. Set to the maximum allowable temperature. Further, the sum of the time t1 during which power is consumed and the time t2 during which power is not consumed corresponds to the time T of one cycle. Considering this, from the formula [11, +21, (
3) An equation is derived.

In equation (3), 01. θF'+ τ8. Since T and τ1 have been determined, the time t during which power is consumed
1 is found. And this 1. is the upper limit T of the on-time of the switching element. This corresponds to □□.

The upper limit value T. The calculation method for NMAX is based on the case where the temperature rise of the resistor R and the switching element TR is the largest. Therefore, the periods during which power is consumed are dispersed during the time T of one cycle. Therefore, according to this embodiment, as described above, the temperature rise of the resistor R and the switching element TR can be suppressed to below the permissible value, and the performance of these elements can be maximized. It can be used for.

Next, an embodiment of the present invention using the fr microcomputer will be described with reference to FIG.

In the figure, the regeneration control circuit 3 is a calculation unit CPU.

The JLI1 device is a microcomputer connected to the ROM, RAM, interface i10, etc., and the rest is the same as the embodiment shown in FIG.

The arithmetic unit CPυ performs various arithmetic processes using processing means stored in advance in the memory TlROM.

The storage devices ROM and RAM store processing procedures necessary for the processing according to the flowchart shown in FIG. 5, various notators such as 'r, TONMA II + tm, etc., and intermediate data necessary for control, such as T. N.

N (described later) is stored.

The interface i10 functions to take in signals given from the outside and to send signals from the arithmetic unit CPU to the outside.

Next, the operation of this embodiment will be explained with reference to the flowchart of FIG.

The calculation unit cpu receives the output of the comparator OP through the interface i10 according to the program in the storage device ROM, and the received signal is a signal indicating that the DC voltage V is larger than the reference value V. When , the calculation unit CPU calculates the cumulative time T for turning on the switching element TR stored in the storage device ZRAM and ROM. , and the upper limit value T of the on-time. HIT□ is read in, and then the two read values are compared and calculated. If the cumulative time TO2 is smaller than the upper limit TONMAM, the calculation unit CPtJ determines the unit time t for turning on the switching element TR stored in the storage RAM.

is read, and the switching element TR is turned on through the interface i10 only during this time. After turning on the switching element TR, the CPU of the arithmetic unit turns on the storage device RA.
The count value N in M is read, 1 is added to this value, and the result is stored in the storage device RAM again. In addition, the value obtained by multiplying this count value N by the unit time [, is also stored in the storage device RAM. After this process is completed, the arithmetic unit CPU goes to read the signal of the comparator OP again through the interface i10, If the DC voltage VD is higher, the above-described process is repeated again. By repeating this process several times, the cumulative time 'rON becomes the upper limit T.

□Thicker than 8 (in this case, the calculation unit CPU is
It is determined that the temperature rise of the switching element TR and the power absorption resistor R is excessive, and without outputting the signal to turn on the switching element TR, the process returns to the process of receiving the output of the comparator OP, and the integrated time ToH and count are This process is repeated until the value N is reset. Mi calculation time T. To reset the count value N and the count value N, when a soft timer created in a separate routine times up, the calculation unit CPU resets the accumulated value T in the storage device RAM. N, count value N is 0
This is performed by storing the data in the storage device RAM again.

Therefore, this embodiment also achieves the same operation as the embodiment shown in FIG. 1 shown in FIG. 2, and as shown in FIG. can.

Note that although the above description has been made regarding the case where a transistor is used as a switching element, it goes without saying that the present invention can also be implemented using other switching elements such as an SCR.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to arbitrarily control the temperature rise of the regenerative power absorption resistor and switching element to an optimal value, thereby eliminating the drawbacks of the conventional technology and eliminating the need for temperature detection and energization time detection. This eliminates the need for protection devices such as relays, and allows the ability of these resistors and switching elements to be used to the maximum, making it easy to create a reversible braking system for inverters with excellent cost performance. Obtainable.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the inverter regenerative braking control device according to the present invention, Fig. 2 is a time chart for explaining the operation, Fig. 3 is an explanatory diagram of temperature rise control, and Fig. 4 is the present invention. FIG. 5 is a block diagram showing another embodiment, FIG. 5 is a flowchart for explaining the operation, and FIG. 6 is a block diagram showing a conventional example of an inverter regenerative braking control device. 1... Voltage source inverter, IA... Forward conversion section,
IB: Inverse conversion section, IC: Capacitor, 2.
... Regeneration control section, 3 ... Regeneration control circuit, 4 ...
・Switching control circuit, 5: Recirculation time output circuit, 6: Periodic control circuit, R: Power absorption resistor, TR: Switching element. Figure 1 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. In a regenerative braking control device for a voltage source inverter equipped with a power absorption resistor on the DC side of an inverse conversion section, the power absorption resistor is connected at a predetermined fixed period for a predetermined fixed period of time. 1. A regenerative braking control device for an inverter, characterized in that a control means for conducting is provided, and the control means controls conduction of the power absorbing resistor during regenerative braking. 2. In claim 1, the control means:
A regenerative braking control device for an inverter, comprising a counter that counts a predetermined clock signal on the condition that the voltage on the DC side of the inverse converter is equal to or higher than a predetermined value, and is cleared at the predetermined constant cycle. .