JP5643951B2 - DC power supply - Google Patents

Description

  The present invention relates to a high-current DC power supply device particularly suitable for use for surface treatment such as electroplating.

  In recent years, DC power supplies for surface treatment such as plating and alumite rectify the supplied commercial AC power, convert the output to high-frequency rectangular AC using an inverter, and convert this rectangular AC to a predetermined voltage. In addition, a system called an inverter system, a switching system, a DC-DC converter system, or the like, which has been rectified to obtain a direct current, has come to be used. These systems have the advantage of good output waveforms, and the use of high-frequency transformers reduces the size of the transformer, which has the advantage of making the entire DC power supply compact and lightweight. There is a tendency.

  In general, it is necessary to measure or control the DC output current with high accuracy, not only for surface treatment, but in the past, it was common to connect a shunt to the DC output side to detect the current. It was. However, the shunt has a large loss and is expensive if it has a large current such as several thousand amperes or more. This causes a problem that the efficiency of the DC power supply device is reduced and the cost is high. In addition, the detection voltage is as weak as 60 mV, for example, and is susceptible to noise. Further, since a large current shunt is large and needs to be cooled, a high frequency transformer is used. As a result, there is a problem that the advantage that the DC power supply device becomes small and light is lost. In order to solve such a problem, for example, a method that does not use a shunt for current detection as shown in Patent Document 1 has been proposed.

  The DC power supply device disclosed in Patent Document 1 is a rectifier that obtains DC from a commercial frequency AC power supply, an inverter that receives the output of the rectifier and outputs a square wave AC of a predetermined frequency, and controls the output of the inverter Control device, a transformer for converting the output voltage of the inverter, and a rectifier for rectifying the secondary output of the transformer, and an output signal of a current measuring device for measuring the output current of the inverter by the control device is input. In the DC power supply device for controlling the output current of the rectifier by controlling the waveform width of the square wave, the control device performs absolute rectification by full-wave rectifying the output signal of the current measuring device as its input signal. Absolute value circuit that obtains a value signal, pulse generation that outputs a pulse signal at the intermediate point between the rising point and falling point of the ON command signal of the inverter A sample / hold circuit that samples and holds the output signal of the absolute value circuit using the pulse signal output from the pulse generator as a sample signal, and the output signal of the sample / hold circuit is proportional to the load current. It is made to do.

  In this configuration, the output signal of the current measuring instrument is sampled and held at the rise and fall times of the inverter on-command signal, that is, at the midpoint of the on-period of the inverter semiconductor switch. It is shown in FIG. However, this figure does not accurately represent the actual situation in that the commutation period of the diode that rectifies the secondary output of the transformer is not shown, and the waveform of each part is actually shown in FIG. It will be like that. In FIG. 2, A is the primary voltage of the transformer, B is the primary current of the transformer, C is the secondary voltage of the transformer, D is the DC output voltage, and E is the DC output current. During the commutation of the diode, the primary current of the transformer gradually increases and decreases during that period, and during this period, a short circuit period is caused by both diodes, so the DC output voltage is also zero volts.

  When the commutation period ends, a period in which the primary current of the transformer and the DC output current are in proportion is continued until the semiconductor switch of the inverter is turned off, during which the primary current of the transformer gradually increases linearly. Therefore, if the primary current of the transformer is detected and sampled and held at a time tn1 or tn2 in the middle of the period in which the primary current of the transformer and the DC output current are proportional, a measurement signal proportional to the DC output current can be obtained. Will be able to. On the other hand, in Patent Document 1, the primary current of the transformer is sampled and held at an intermediate point of the ON period of the semiconductor switch of the inverter, and the measured current value and the actual value are shifted because the sample and hold point is shifted. There is a problem that a difference occurs between the current values.

In order to solve this problem, a method of correcting by shifting the time point of sample hold by providing a delay time or the like can be considered. However, especially in a low-voltage, high-current DC power supply device for surface treatment, the commutation period is long, and the length of the commutation period changes when the AC input voltage fluctuates. It also changes when the DC output voltage and current change due to changing settings or changing the load. Corresponding to the change in the length of the commutation period, it is practically impossible to correct the sample and hold time by appropriately shifting, and the one in Patent Document 1 can measure the DC current with high accuracy. There wasn't.
Japanese Patent Laid-Open No. 5-38158

  The present invention has been made to solve the above-mentioned problems and to provide a DC power supply device capable of measuring the DC output current with high accuracy without using a shunt by measuring the primary current of the transformer. It is.

  The invention of claim 1 made to solve the above problem includes a first rectifier circuit for rectifying a commercial power supply, a single-phase inverter for converting the output of the first rectifier circuit into an alternating current, In a DC power supply device comprising a transformer for stepping down the output and a second rectifier circuit for rectifying the secondary output of the transformer, a current transformer for detecting the primary current of the transformer, and a current by the current transformer A sample and hold command signal is supplied to the sample and hold means at an intermediate point between the sample and hold means for sampling and holding the detection signal and the time when the commutation of the second rectifier circuit is completed until the semiconductor switch constituting the inverter is turned off. A command signal generating means is provided, and the output signal of the sample hold means is a signal proportional to the DC output current of the DC power supply device. Here, it is possible to provide detection means for detecting the end of the commutation period of the second rectifier circuit by detecting the rise of the output voltage of the second rectifier circuit.

  According to the present invention, the primary current of the transformer is sampled and held at an intermediate point between the end of commutation of the second rectifier circuit and the semiconductor switch constituting the inverter is turned off, Therefore, even if the length of the commutation period changes, there is an advantage that it can be accurately measured.

Next, the best mode for carrying out the present invention will be specifically described with reference to the drawings.
FIG. 1 is a connection diagram of a main circuit showing the configuration of the present invention. A DC power source for converting AC power supplied from an AC input terminal 3 by a rectifier 1 and a capacitor 2 as a first rectifier circuit into DC power is shown. It is provided. The positive poles of the semiconductor switches 4a and 4b are connected to the positive pole of the DC power supply, and the negative poles of the semiconductor switches 4a and 4b are connected to the negative poles of the semiconductor switches 5a and 5b, respectively. The positive pole is connected. These semiconductor switches 4a, 4b, 5a and 5b constitute a single-phase inverter.

  The primary coil of the transformer 6 is connected between the connection point of the semiconductor switches 4a and 5a and the connection point of the semiconductor switches 4b and 5b, which are output terminals of the single-phase inverter, and the secondary coil of the transformer 6 A center tap is provided, and anodes of diodes 7a and 7b are respectively connected to both ends to constitute a second rectifier circuit. The cathodes of the diodes 7a and 7b are connected to the positive DC output terminal 8a, and the center tap of the transformer 6 is connected to the negative DC output terminal 8b. 9 is a current transformer which detects the current of the primary coil of the transformer 6.

  The current transformer 9 can be a general one in which a secondary coil is wound around a toroidal core, and the primary coil of the current transformer 9 has a wire passing through the primary coil of the transformer 6. However, it is preferable that the high-frequency characteristics are good. The current on the primary side of the transformer 6 detected by the current transformer 9 and the voltage of the DC output output to the DC output terminals 8a and 8b are connected so as to be input to the control device 10, respectively. The control device 10 includes a drive signal generation circuit that generates drive signals for the semiconductor switches 4a, 5b, 5a, and 5b, a DC output control circuit that controls the DC output, and the primary of the transformer 6 detected by the current transformer 9. There is provided sample hold means for sample-holding the current on the side, and command signal generating means for supplying a sample hold command signal to the sample hold means.

  The drive signal generation circuit alternately supplies drive signals to the set of semiconductor switches 4a and 5b and the set of semiconductor switches 4b and 5a, and the DC output control circuit uses the semiconductor switches 4a and 5b and the semiconductor switches by PWM control or the like. The fact that the DC output is controlled by changing the duty of the on-time of 4b and 5a is the same as that of the conventional DC power supply device of such a system, and can have the same configuration as the conventional one. On the other hand, the sample hold means and the command signal generating means are characteristic of the present invention, and the configuration and operation including the same parts as the conventional one will be described below.

  FIG. 2 shows the waveform of the main part of the DC power supply device of the present invention, where the horizontal axis represents the passage of time, A is the primary voltage of the transformer 6, B is the primary current of the transformer 6, and C is the transformer. The secondary voltage of the device 6, D is the DC output voltage, and E is the DC output current. The period from t1 to t3 is a period in which the semiconductor switches 4a and 5b are on, and the power supply voltage is applied to the primary coil of the transformer 6 during that period. From t1 to t2 is a commutation period in which the current flowing in the diode 7b is transferred to the diode 7a, and the secondary coil of the transformer 6 is short-circuited by the diode 7a and the diode 7b. No voltage appears on the coil. During this time, the primary current of the transformer 6 gradually increases.

  t2 is the commutation end point at the end of the commutation period, and is released from the short circuit by the diode 7a and the diode 7b, a voltage is generated in the secondary coil of the transformer 6, and is output to the DC output terminals 8a and 8b through the diode 7a. The The period from t2 to t3 is a period in which power is supplied from the primary side of the transformer 6 to the DC output. The primary current of the transformer 6 gradually increases linearly, and the primary current and DC output current of the transformer 6 during this period are Proportional relationship. t3 is a turn-off time when the semiconductor switches 4a and 5b are turned off, and from t3 to t4 is a commutation period in which the current flowing in the diode 7a is transferred to the diode 7b. At time t4, a current is flowing through both the diodes 7a and 7b.

  Similarly, the period from t5 to t6 is a period in which the semiconductor switches 4b and 5a are on, and the power supply voltage is applied to the primary coil of the transformer 6 with a reverse polarity. From t5 to t6 is a commutation period in which the current flowing in the diode 7a is transferred to the diode 7b, no voltage appears in the secondary coil of the transformer 6, and the magnitude of the primary current of the reverse polarity of the transformer 6 is large. The gradual increase. t6 is the end of commutation, and a voltage having a reverse polarity is generated in the secondary coil of the transformer 6 and is output to the DC output terminals 8a and 8b through the diode 7b. The period from t6 to t7 is a period in which power is supplied from the primary side of the transformer 6 to the DC output. The magnitude of the primary current of the transformer 6 gradually increases linearly, and the magnitude of the primary current of the transformer 6 during this period. And the DC output current have a proportional relationship. t7 is a turn-off time when the semiconductor switches 4b and 5a are turned off, and from t7 to t8 is a commutation period in which the current flowing in the diode 7b is transferred to the diode 7a. At time t8, the current flows through both the diodes 7a and 7b. Thereafter, such an operation is continuously repeated.

  The waveform of each part changes as described above, and after the commutation period between the diodes 7a and 7b ends, until the semiconductor switches 4a and 5b or the semiconductor switches 4b and 5a are turned off, that is, from t2 to t3 or t6. From t to t7, the magnitude of the primary current of the transformer 6 and the DC output current are in a proportional relationship. Therefore, the primary current of the transformer 6 is detected and sampled and held at an intermediate time tn1 or tn2 between t2 and t3 or between t6 and t7 where the magnitude of the primary current of the transformer 6 and the DC output current are in a proportional relationship. Then, a measurement signal whose absolute value is proportional to the DC output current can be obtained.

  FIG. 3 shows an example of the configuration of the sample and hold means. The input terminals of the first sample and hold circuit 11a and the second sample and hold circuit 11b are connected to the current signal input terminal 12a. 12b is a current signal input terminal on the return side, and the secondary coil of the current transformer 9 is connected to the current signal input terminals 12a and 12b. Reference numeral 13 denotes a terminal resistance of the current transformer 9. The input terminal of the polarity inversion circuit 21 is connected to the output terminal of the second sample hold circuit 11b, and the output terminal of the first sample hold circuit 11a and the output terminal of the polarity inversion circuit 21 are input to the average value circuit 14. It is connected to the terminal. Reference numeral 15 denotes a third sample and hold circuit having an input terminal connected to the output terminal of the average value circuit 14.

  FIG. 4 shows an example of a detection circuit for detecting the end of the commutation period. The input terminal of the comparator 17 is connected to the voltage signal input terminal 19a via the waveform shaping circuit 18. The waveform shaping circuit 18 is constituted by a constant current diode and a constant voltage diode, for example, and limits an input signal whose amplitude changes to a constant amplitude. Reference numeral 19b denotes a voltage signal input terminal on the return side, and the voltage signal input terminals 19a and 19b are connected to the DC output terminals 8a and 8b, respectively. As shown in FIG. 2D, the DC output voltage rises when the commutation period ends, and becomes zero when the semiconductor switch is turned off. Therefore, the time points t2 and t6 can be detected, and the semiconductor switches 4a and 4b are detected. The timing signals t2 and t6 can be separated by a logical operation with the drive signals 5a and 5b.

  The DC output control circuit includes a counter that counts a clock during the ON period of the semiconductor switch, a calculator that compares the DC output voltage or DC output current with a set value, calculates an error, and provides a command value for the ON period of the semiconductor switch. The comparator is configured to compare the command value with the count value of the counter, the semiconductor switch is turned on and counting by the counter is started, and the comparator detects that the count value of the counter has reached the command value. By the way, by turning off the semiconductor switch, the semiconductor switch is turned on for a period corresponding to the command of the arithmetic unit. The counter starts counting at t1 or t5 when the semiconductor switch is turned on, and when the counter count value reaches the command value at t3 or t7, the semiconductor switch is turned off.

  The DC output control circuit further includes a storage circuit that stores the count value of the counter, an arithmetic unit that calculates an intermediate command value corresponding to an intermediate time point by subtracting the storage value of the storage circuit from the command value of the ON period, A comparator for comparing the intermediate command value with the count value of the counter is provided. The memory circuit stores the count value of the counter at the time t2 or t6 by the end detection signal of the commutation period, and the arithmetic unit subtracts the memory value of the memory circuit from the command value during the ON period, between t2 and t3 or t6− The count value during t7 is calculated. Since the intermediate command value corresponding to the time point tn1 or tn2 is obtained from this, the comparator detects the time point when the intermediate command value and the count value of the counter coincide with each other, and at the time point tn1, the first sample hold circuit 11a receives the tn2 At this time, a sample hold command signal is given to the second sample hold circuit 11b.

  In this way, the primary current detected by the transformer 6 detected by the second sample and hold circuit 11b at the time tn1 is sampled and held in the first sample and hold circuit 11a and measured in proportion to the DC output current. A signal can be obtained. Here, the measurement signal obtained from the second sample and hold circuit 11b has the opposite polarity, but the polarity is inverted by the polarity inversion circuit 21 to have the same polarity. From the average value circuit 14, the average value of two consecutive half cycles is obtained. For example, the third sample and hold circuit 15 may sample and hold at a time such as t3 and t7, or may continuously output an input signal.

  Further, the sample hold means may be a changeover switch instead of the average value circuit 14 and the third sample hold circuit 15. In this case, the output of the first sample and hold circuit 11a is selected for the positive half-wave, and the output of the second sample and hold circuit 11b is selected for the negative half-wave. is there. The polarity inversion circuit 21 connected to the output side of the second sample and hold circuit 11b can also be connected to the input side of the second sample and hold circuit 11b.

It is a wiring diagram of the main circuit which shows the structure of this invention. It is a wave form diagram of the principal part at the time of operation. It is a connection diagram which shows the structure of a current calculation circuit. It is a connection diagram which shows the structure of the detection circuit which detects the end of a commutation period.

DESCRIPTION OF SYMBOLS 1 Rectifier 2 Capacitor 3 AC input terminal 4a, 4b, 5a, 5b Semiconductor switch 6 Transformer 7a, 7b Diode 8a, 8b DC output terminal 9 Current transformer 10 Controller 11a, 11b Sample hold circuit 12a, 12b Current signal input terminal 13 Terminating resistor 14 Average value circuit 15 Sample hold circuit 16 Current signal output terminal 17 Comparator 18 Waveform shaping circuit 19a, 19b Voltage signal input terminal 20 Detection signal output terminal 21 Polarity inversion circuit

Claims (2)

  A first rectifier circuit that rectifies commercial power, a single-phase inverter that converts the output of the first rectifier circuit into alternating current, a transformer that steps down the output of the inverter, and a secondary output of the transformer is rectified In a DC power supply device comprising a second rectifier circuit, a current transformer for detecting a primary current of the transformer, a sample hold means for sample-holding a current detection signal from the current transformer, and a second rectifier circuit There is provided a command signal generating means for giving a sample hold command signal to the sample hold means at an intermediate time from the commutation end time to the time when the semiconductor switch constituting the inverter is turned off, and the output signal of the sample hold means is a DC power supply device A direct current power supply device characterized in that the signal is proportional to the direct current output current.   2. The DC power supply device according to claim 1, further comprising detection means for detecting the end of the commutation period of the second rectifier circuit by detecting the rising of the output voltage of the second rectifier circuit.

Images