JP4786244B2 - AC power controller - Google Patents

Description

  The present invention relates to an AC power control device that performs phase control of AC power supplied to a load such as a heater for an electric furnace by firing angle control by a power semiconductor element.

  As this type of AC power control apparatus, an AC power control apparatus having a structure described in Patent Document 1 below is known. This AC power control device basically includes a power control unit having a power semiconductor element such as a thyristor connected in series to a power supply line, a gate drive circuit that outputs a trigger signal to the power control unit, a load A firing angle control signal corresponding to the power supplied to the load is generated in accordance with a difference signal between the detection signal of the power supplied to the target signal and the target signal or a command signal input from a manual switch or the like. A main control unit that generates a pulse signal at a time delayed from a reference point (zero cross point) by a control angle corresponding to the firing angle control signal, and outputs the pulse signal to the gate drive circuit.

Then, the main control unit calculates a timer value of the ignition angle signal serving as an output signal based on, for example, a command signal sent from the temperature controller, and controls the timer value from the reference point (zero cross point) of the power supply voltage. A pulse signal is generated when the angle is delayed, and the pulse signal is output to the gate drive circuit. In response to this, the gate drive circuit outputs a trigger signal to the power semiconductor element of the power control unit, thereby It operates to control the power of the furnace heater.
Japanese Patent Laid-Open No. 10-41051

  Such control of AC power is performed by calculation using digital calculation means such as a microcomputer, and a command signal sent from the temperature controller is applied as an analog command signal having a current value of 4 mA to 20 mA, for example, and is usually 1000 An A / D converter that samples input data by division and converts it to digital is used. The analog command signal is converted into a digital signal and input to the digital calculation means of the main control unit, and the main control unit performs PID calculation and the like to calculate a timer value (ignition angle data).

  From the viewpoint of manufacturing cost, for example, an A / D converter that samples input data in 1000 divisions and converts it to digital is used for the control A / D converter. Such an A / D converter is used. In this case, as shown in the graph of FIG. 6, the firing angle control signal as an output changes from 0% to 100% with respect to the command value of 4 mA to 20 mA of the command signal input from the temperature controller, During this period, control is performed with a resolution of 1000 divisions.

  That is, since the resolution of 1000 divisions is fixed as an upper limit by the resolution of the A / D converter used in the main control unit, 0% to 100% of the output ignition angle control signal (ignition angle control amount) % Range is divided into 1000, and the fineness of the control amount that is actually controlled, that is, as shown in FIG. 6, the change amount Δd of the minimum unit of the output firing angle control signal is 0. It will be limited to 1%.

  For this reason, when there is a change of less than 0.1% in the command value sent from the temperature controller, the power control corresponding to the change in the load cannot be performed, and the load cannot be controlled with high accuracy. There was a problem.

  The present invention has been made in view of the above points, and even when the resolution of power control is limited to a low level, an AC power control apparatus capable of performing output control of AC power more finely within the range of the resolution. The purpose is to provide.

In order to achieve the above object, an AC power control apparatus according to the present invention includes a power control unit in which power semiconductor elements are connected in series to a power supply line, and a gate drive circuit that outputs a trigger signal to the power control unit. And a main controller that calculates a firing angle control amount corresponding to the power supplied to the load based on a command signal given from the outside, and outputs a pulse signal corresponding to the firing angle to the gate drive circuit. In the AC power control device,
An offset value setting means for setting and inputting a lower limit value of the firing angle control amount as an offset value in an output graph showing a relationship between the control command amount given by the command signal and the firing angle control amount;
A gradient value setting means for setting and inputting a gradient value for determining a control range of the firing angle control amount and a gradient of the output graph ;
Basic firing angle control amount calculating means for calculating a basic firing angle control amount from at least one of the offset value and the gradient value and the control command amount;
A firing angle control amount calculating means for calculating a firing angle control amount by performing a PID calculation on the basic firing angle control amount;
Timer value conversion means for converting the ignition angle control amount into a timer value as ignition angle data;
An ignition pulse output means for outputting an ignition pulse signal to the gate drive circuit based on the timer value;
With
When said load becomes a stable state, reads the gradient value lower limit value of the firing angle control amount read from the offset setting means as the offset value, or / from及beauty the gradient value setting means in the output graph, the by calculating the basic firing angle control amount using the at least one of the offset value and the gradient value and a control instruction value, and performing narrowing of the output distribution of the firing angle control.
Here, the gradient value is a percentage value that is set to narrow the control region and determines the control range of the firing angle control amount and the gradient of the output graph.

  Here, the load is a heater for the electric furnace, and when the command signal is output from the temperature controller of the electric furnace and the temperature fluctuation of the load is reduced and becomes stable, the stable operation from the temperature controller is performed. Can be configured to be output to the main control unit.

The main control unit of the AC power control apparatus having the above configuration, when the fluctuation of the load is reduced and becomes a stable state, determines the relationship between the control command amount given by the command signal and the firing angle control amount from the offset value setting means. The lower limit value of the output graph shown is read as an offset value, and the gradient value that determines the control range of the firing angle control amount and the gradient of the output graph is read from the gradient value setting means. Then, the basic firing angle control amount calculating means calculates the basic firing angle control amount from at least one of the offset value and the gradient value and the control command amount of the command signal given from the outside.

At this time, when the basic firing angle control amount means calculates the basic firing angle control amount from the control command amount of the command signal, the lower limit value of the output graph showing the relationship between the control command amount and the firing angle control amount is For example, when the basic firing angle control amount is calculated by setting 50% as the offset value, setting the control range of the firing angle control amount and the gradient value that determines the gradient of the output graph as 50%, the control command amount As shown in FIG. 5, in the output graph showing the relationship between the ignition angle control amount and the ignition angle control amount, the control range of the ignition angle control amount can be narrowed from the lower limit value 50% to the upper limit value 75% with respect to the entire control command amount. it can. For example, when a 1000-divided A / D converter is used and the range of the output ignition angle control amount is changed from the normal lower limit value 0% to the upper limit value 100%, as shown in FIG. The command amount per hit is 0.1%, but by narrowing the control region from the lower limit value 50% of the ignition angle control amount to the upper limit value 75%, as shown in FIG. It is possible to finely control the command amount per unit to 0.025%.

  Next, the ignition angle control amount calculation means performs a PID calculation on the basic ignition angle control amount to calculate a further improved ignition angle control amount. Then, the timer value conversion means converts the ignition angle control amount into a timer value as the ignition angle data, and the ignition pulse output means outputs an ignition pulse signal to the gate drive circuit based on the timer value. The power semiconductor element of the power control unit is turned on at the firing angle controlled by the gate drive circuit, and AC power is supplied to the load.

  Thus, by narrowing down the control output region, for example, AC power supplied to a load such as an electric heater can be more finely controlled according to a control command amount sent from a temperature controller or the like. Also, use an A / D converter that performs A / D conversion of a control command amount sent from a temperature controller or the like without using a high-resolution, high-cost one with a normal resolution. Manufacturing cost can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an AC power control apparatus. In FIG. 1, reference numeral 1 denotes a power supply line for supplying single-phase AC power to, for example, an electric furnace heater as a load 2, and a power control unit 3 in which a power semiconductor element such as a thyristor is connected in reverse parallel to the power supply line 1. Connected in series. A CR absorber is connected to the power semiconductor element as a surge killer.

  A gate drive circuit 4 that outputs a trigger signal is connected to the power control unit 3, and the gate drive circuit 4 is controlled by a main control unit 5 built in a control panel or the like. An ignition pulse signal is output to the gate drive circuit 4 at the calculated timing.

  As shown in FIG. 1, the main control unit 5 is configured with a microcomputer as a main part, and includes an input / output circuit including a CPU, a ROM, a RAM, an A / D converter, an electrically rewritable EEPROM, and the like. The memory 13 is provided. The CPU, based on the program data stored in advance, based on the control command amount In input from the temperature controller 10 as described later, the firing angle controlled in accordance with the power to be supplied to the load 2. A process of outputting a pulse signal to the gate drive circuit 4 is performed.

  The temperature controller 10 is provided, for example, in an electric furnace of an electric furnace heater serving as a load, and a feedback control signal is output as a control command amount signal from the controller of the temperature controller 10, and is sent to the main control unit 5 as a control command amount In. Entered. A signal indicating the control command amount In, a current detection signal, a voltage detection signal, and the like are taken into the CPU of the main control unit 5 via an A / D converter built in the input / output circuit of the main control unit 5. Further, when the temperature in the electric furnace reaches the vicinity of the set temperature and becomes a stable operation state, a signal indicating the stable operation is output from the temperature controller 10 to the main controller 5.

  Further, the main control unit 5 is connected to an offset setter 11 for setting and inputting an offset value Os for calculating a firing angle control amount, which will be described later, and a gradient value indicating the gradient of the output graph used for the calculation. A gradient setter 12 for setting and inputting G is connected. The offset setting unit 11 and the gradient setting unit 12 are configured using, for example, a variable resistor, and the user can set the offset value Os or the gradient value G as an arbitrary% value. Further, a manual setting device 19 for manually setting the control command amount instead of the control command amount of the temperature controller 10 is connected to the main control unit 5, and further, the operation of the control device is automatically switched between automatic and manual. A manual switch 14 is connected to the main control unit 5. When the automatic / manual switching device 14 is automatic, a control command amount is sent from the temperature controller 10 to the main control unit 5, and when the automatic / manual switching device 14 is switched to manual, the control command amount is sent from the manual setting device 19. Is sent to the main control unit 5.

  Further, when the load 2 is stabilized and a signal indicating it is input from the temperature controller 10 during the automatic operation, the main control unit 5 controls the control given by the command signal from the offset setting unit 11 that sets the offset value Os. The lower limit value of the output graph indicating the relationship between the command amount and the ignition angle control amount is read as the offset value Os, and the gradient value G indicating the gradient of the output graph is read from the gradient setting unit 12.

  Then, the basic firing angle control amount Ox is calculated from the following equation from the offset value Os, the gradient value G, and the control command amount In of the command signal given from the temperature controller 10.

Ox = Os + (In × Δk × G / 100)
Here, Δk is the slope of the output graph. For example, in the output graph of FIG. 3, the firing angle control amount Ox as an output is 50% to 100% with respect to the control command amount In of 0 to 1000, The slope Δk of the output graph is 0.05.

  Further, the main control unit 5 performs a PID operation on the basic firing angle control amount Ox to calculate a further improved firing angle control amount Oxpid. The PID calculation is a calculation that converges to a set value by combining proportional calculation, integration calculation, and differentiation calculation. Then, the ignition angle control amount Oxpid is converted into a timer value as the ignition angle data, and an operation is performed so as to output an ignition pulse signal to the gate drive circuit 4 based on the timer value.

  That is, the main control unit 5 receives a zero cross detection signal from the zero cross point detection circuit 9 and generates a pulse signal having a predetermined width from the reference point (zero cross point) of the power supply voltage with a control angle corresponding to the timer value. , And operates to output to the gate drive circuit 4. The ROM of the main control unit 5 stores in advance a data table indicating the relationship between the ignition angle control amount Oxpid and the timer value, and converts the ignition angle control amount Oxpid into a timer value using the table data. To do.

  On the other hand, a current detector 7 for detecting a current supplied to the load 2 is connected to the power supply line 1 through a current transformer, and a current value detected by the current detector 7 is input to the main control unit 5. . Further, a voltage detector 8 that detects the voltage of the supply line is connected to the power supply line 1 via a voltage transformer, and the voltage value detected by the voltage detector 8 is input to the main controller 5. The power supply line 1 is connected to a zero-cross point detection circuit 9 that detects a zero-cross point of the potential, and the output side of the zero-cross point detection circuit 9 is connected to the main control unit 5.

  Furthermore, the main control unit 5 outputs a soft start / soft down setting device (variable resistor) 15 and an alarm output that outputs an alarm when the fuse 18 is disconnected or when the current detector 7 detects an overcurrent. A circuit 16 is connected. Further, a display 17 for displaying the voltage value, current value, various set values, operation mode, and the like of the power supply line 1 detected as described above is connected to the main control unit 5.

  Next, the operation of the AC power control apparatus having the above configuration will be described. Prior to driving, the user operates the offset setting device 11 to set the offset value Os, and operates the gradient setting device 12 to set the gradient value G. The offset value Os and the gradient value G can be set by setting at least one set value or both according to the control region to be narrowed down.

  The set of the offset value Os and the gradient value G indicates the firing angle control amount output from the main control unit 5 when the measured temperature in the furnace reaches the target temperature and stabilizes when the electric furnace is operated. The value is narrowed down to the range of the firing angle control amount Ox of the output graph as shown in FIGS. 3 to 5 so that fine control can be performed.

  The offset value Os indicates the lower limit value of the output graph. For example, in the output graph shown in FIG. 3, the offset value Os is set to 50%. When the resolution of the input control command amount In (resolution of the A / D converter that converts the command signal into a digital signal) is 1000 divisions, the slope Δk of the output graph is 0.05, and the output firing angle The minimum change amount Δd of the control amount is 0.05%. Therefore, it is narrowed down to a range that is half that of the case where the normal minimum change Δd is 0.1%, and the fluctuation range of the input control command amount In can be finely controlled to 0.05%.

  Further, when the gradient value G is set to 50% in the gradient setting unit 12, as shown in the output graph of FIG. 4, the resolution of the input control command amount In (A / D converter that converts the command signal into a digital signal) When the resolution is 1000 divisions, the slope Δk of the output graph is 0.05, and the minimum change amount Δd of the firing angle control amount to be output is 0.05%. Therefore, it is narrowed down to a range that is half that of the case where the normal minimum change Δd is 0.1%, and the fluctuation range of the input control command amount In can be finely controlled to 0.05%.

  Further, when the gradient value G is set to 50% in the gradient setter 12 and the offset value Os is set to 50% in the offset setter 11, as shown in the output graph of FIG. When the resolution of In (the resolution of the A / D converter that converts the command signal into a digital signal) is 1000 divisions, the slope Δk of the output graph is 0.025, and the minimum change amount of the output firing angle control amount Δd is 0.025%. Therefore, the range of the control command amount In is narrowed down to a range of 1/4 compared with the case where the normal minimum change amount Δd is 0.1%, and the output can be finely controlled up to a fluctuation range of 0.025%.

  This will be described with reference to the flowchart of the output process of FIG. 2. First, in step 100, the CPU of the main control unit 5 determines whether or not the temperature of the electric furnace is stable near the target temperature. For example, if it is determined that the temperature is stable based on the measured temperature information sent from the temperature controller 10 of the electric furnace, the process proceeds to step 110. In step 110, the main control unit 5 captures the control command amount In sent from the temperature controller 10, and in the case of FIG. 3, captures a preset offset value Os (50%). On the other hand, in the case of FIG. 4, the gradient value G (50%) is captured, and in the case of FIG. 5, the offset value Os (50%) and the gradient value G (50%) are captured. Further, the current value of the power supply line input through the current detector 7 and the voltage detector 8, the measured value data of the voltage, and the like are captured.

  Next, the routine proceeds to step 120, where the offset value Os, the gradient value G, and the control command amount In of the command signal from the temperature controller 10 are used to calculate Ox = Os + (In × Δk × G / 100). The basic firing angle control amount Ox is calculated. That is, the basic firing angle control amount Ox (%) is calculated by multiplying the control command amount In of the command signal by the percentage of the gradient Δk and the gradient value G and adding the offset value Os thereto. Here, in the case of FIG. 3, the basic firing angle control amount Ox is calculated with the gradient value G being 100%, and in the case of FIG. 4, the basic firing angle control amount Ox is calculated with the offset value Os being 0%. Then, the basic ignition angle control amount Ox is PID-calculated to calculate a further improved ignition angle control amount Oxpid.

  Next, in step 130, the ignition angle control amount Oxpid is converted into a timer value To using, for example, a data table indicating the relationship between the ignition angle control amount Oxpid and the timer value. Set the timer value To.

  On the other hand, in the zero cross point interrupt process, the CPU of the main control unit 5 first determines in step 200 whether or not the potential of the supply line has reached the zero cross point, and the potential is zero crossed by detection by the zero cross detector 9. When it is determined that a point has been reached, in step 210, the timer value To calculated above is set in the timer counter, and counting is started.

  Then, in the timer interruption process, it is determined in step 300 whether or not the count value of the timer counter has reached the set timer value. When the count time has reached the set timer value, the main control unit 5 A pulse signal is output to the gate drive circuit 4, and the gate drive circuit 4 makes the power semiconductor element of the power control unit 3 conductive by the firing angle pulse signal. That is, the gate drive circuit 4 generates a trigger signal in synchronization with the rise of the pulse signal and outputs it to the gate of the power semiconductor element of the power control unit 3. The power semiconductor element of the power supply line 1 is turned on by a trigger and operates so as to turn on to the next zero cross point, and the power supplied to the load 2 is controlled by such ignition angle control (phase control). .

  Thus, when calculating the firing angle control amount Ox with respect to the input control command amount In, the offset value Os is set to increase the lower limit value of the output graph, or the gradient is changed to change the gradient of the output graph. In order to narrow the control output region by setting a value, the AC power supplied to the load 2 can be controlled more finely according to the control command amount sent from the temperature controller 10. In addition, the A / D converter that performs A / D conversion of the control command amount can use a low-cost one with a normal resolution without using a high-resolution and high-cost one, thereby reducing the manufacturing cost. Can be suppressed.

  In the above embodiment, the example in which the electric furnace heater of the electric furnace is used as the load has been described, but the present invention can be applied to other loads. In addition, the automatic control is shifted to the control range as described above based on the signal from the temperature controller 10 during the automatic operation. However, the automatic operation is performed when the temperature of the electric furnace is stabilized during the manual operation. It is also possible to operate so as to shift to control with a narrowed control area. Furthermore, although the single-phase AC power supply line has been described with reference to FIG. 1, the same can be applied to a three-phase AC power supply line.

It is a block diagram of the alternating current power control apparatus which shows one Embodiment of this invention. 4 is a flowchart showing output processing of the main control unit 5 and the like. It is a graph which shows the relationship between the control command amount In (input) and the firing angle control amount Ox (output) when the lower limit value is an offset value of 50%. It is a graph which shows the relationship between the control command amount In (input) and the firing angle control amount Ox (output) when the gradient value G is 50%. It is a graph which shows the relationship between the control command amount In (input) and the firing angle control amount Ox (output) when the lower limit value is 50% offset value and the gradient value G is 50%. It is a graph which shows the relationship between the command value of the conventional input command signal, and an output firing angle control signal.

Explanation of symbols

1-Power supply line 2-Load 3-Power control unit 4-Gate drive circuit 5-Main control unit 9-Zero cross detector 10-Temperature controller 11-Offset setter 12-Gradient setter

Claims (2)

A power control unit in which power semiconductor elements are connected in series to a power supply line, a gate drive circuit that outputs a trigger signal to the power control unit, and a power supplied to a load based on a command signal given from the outside A main control unit that calculates a starting angle control amount and outputs a pulse signal corresponding to the starting angle to the gate drive circuit,
An offset value setting means for setting and inputting a lower limit value of the firing angle control amount as an offset value in an output graph showing a relationship between the control command amount given by the command signal and the firing angle control amount;
A gradient value setting means for setting and inputting a gradient value for determining a control range of the firing angle control amount and a gradient of the output graph ;
Basic firing angle control amount calculating means for calculating a basic firing angle control amount from at least one of the offset value and the gradient value and the control command amount;
A firing angle control amount calculating means for calculating a firing angle control amount by performing a PID calculation on the basic firing angle control amount;
Timer value conversion means for converting the ignition angle control amount into a timer value as ignition angle data;
An ignition pulse output means for outputting an ignition pulse signal to the gate drive circuit based on the timer value;
With
When said load becomes a stable state, reads the gradient value lower limit value of the firing angle control amount read from the offset setting means as the offset value, or / from及beauty the gradient value setting means in the output graph, the by calculating the basic firing angle control amount using the at least one of the offset value and the gradient value and the control instruction values, AC and performing narrowing of the output distribution of the firing angle control Power control device.   The load is a heater for an electric furnace, and the command signal is output from the temperature controller of the electric furnace, and when the temperature fluctuation of the load decreases and becomes a stable state, a signal indicating stable operation from the temperature controller Is transmitted to the main control unit.

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