JP2002291285A - Pwm current detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PWM current detection device for obtaining an instantaneous value of an alternative current waveform superimposing a direct current component by precisely estimating and calculating by means of the output waveform, not using a direct current magnetic flux detection means such as a Hall element. SOLUTION: The device is provided with a pressing element series circuit to be energized in one way by on-off control, an encirculating element to be energized in one way and connected in reverse-parallel to the pressing element, a current transformer for detecting only the alternating component of current flowing to load, for detecting the current flowing to load when the pressing element is PWM controlled, by connecting DC power source to both ends of the pressing element series circuit, connecting one end of the load to the mutual connecting points of the pressing element, and connecting the other end of the load to a prescribed point regarded as the voltage range of the DC power source, and a detected value correction means for correcting the detected value of the current transformer to be output, executing semidriven PWM control for a prescribed region including the region where current flows to the encirculating element by the induction of load and regarding the detected value of which the absolute value of the time variation rate of the current transformer is regarded substantially zero to be a zero level of the current flowing to load.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PWM (Puls) supplied to a load via a power converter for converting DC to AC.
The present invention relates to a PWM current detection device that detects current using a current transformer.

[0002]

2. Description of the Related Art For example, in a motor for driving a compressor, a load torque changes periodically, and a DC component (hereinafter, also referred to as an offset current) is superimposed on a winding current in accordance with the load torque. In order to perform vector control of such a motor, it is necessary to detect an instantaneous value of a current superimposed on an AC fundamental wave component with high accuracy. A current transformer called a DCCT using a Hall element can detect such an instantaneous value of the current while being insulated from a winding of a motor or a power supply line to the motor.

[0003]

However, in the above-described current transformer using the Hall element, the characteristics change due to the temperature of the Hall element and the presence of distortion due to external conditions such as a magnetic field and current for operating the Hall element cause a high level. Various corrections were required to extract the current waveform with high accuracy. In addition, adjustments have to be made for each product due to variations in individual assembly structures and elements. Further, there is also a problem that it is difficult to apply to general home electric appliances because it is expensive.

The present invention has been made in view of the above circumstances, and does not use a DC magnetic flux detecting means such as a Hall element, but uses a current transformer conventionally used in general to obtain an AC current in which a DC component is superimposed. It is an object of the present invention to provide a PWM current detecting device that accurately estimates and calculates an instantaneous value of a current waveform from its output waveform.

[0005]

Means for Solving the Problems According to claim 1 of the present invention,
An energizing element series circuit formed by serially connecting energizing elements that can be energized in one direction by ON / OFF control, and a reflux element that can be energized in one direction and connected in anti-parallel to the energizing element. Among the power conversion units provided, the positive terminal of the DC power supply is connected to the positive terminal of the energizing element series circuit, the negative terminal of the DC power source is connected to the negative terminal, and one end of the load is connected to the interconnection point of the energizing elements, The other end of the load is connected to a predetermined point regarded as a voltage range of the DC power supply, and in a PWM current detection device that detects a current flowing to the load when the energizing element is PWM-controlled, only an AC component of a current flowing to the load is detected. In a predetermined section including a section in which a current flows through the return element due to the induction action of a current transformer and a current inductively detected in a DC state, the biasing element connected in anti-parallel to the return element is turned off. Executes half-drive PWM control In the holding section, a detection value in which the absolute value of the time change rate of the current transformer is regarded as substantially zero is regarded as a zero level of the current flowing through the load, and the detection value of the current transformer is corrected and output. Means.

According to a second aspect of the present invention, in the PWM current detecting device according to the first aspect, the absolute value of the time change rate of the current transformer does not become substantially zero even when the energizing element is kept in the off state. In the section predicted to be, even in a predetermined section including a section in which current flows through the reflux element, full drive PWM control for enabling the energizing element connected in anti-parallel to the reflux element to be turned on is performed. It is characterized by the following.

According to a third aspect of the present invention, in the PWM current detecting device according to the first or second aspect, the current flowing through the load among the detected values in which the absolute value of the time change rate of the current transformer is considered to be substantially zero. The detection value when the fundamental wave component changes from positive to negative and the detection value when the fundamental wave component changes from negative to positive are calculated separately, and the average value is calculated. When the wave component changes from positive to negative and when the wave component changes from negative to positive, the current is set to the zero level.

According to a fourth aspect of the present invention, in the PWM current detecting apparatus according to any one of the first to third aspects, the absolute value of the time rate of change of the current transformer is one of the detected values considered to be substantially zero. The average value of the latest plurality of detection values is used as the correction value.

According to a fifth aspect of the present invention, in the PWM current detecting device according to any one of the first to third aspects, the PWM current detecting device corresponds to a plurality of cycle intervals or a plurality of cycles of a fundamental component of a current flowing through a load. The detection value of the current transformer is corrected at time intervals.

According to a sixth aspect of the present invention, in the PWM current detector according to any one of the first to fifth aspects, an output of the detection value correction means is an input for vector-controlling a three-phase DC brushless motor. It is characterized by information.

According to a seventh aspect of the present invention, in the PWM current detector according to any one of the first to sixth aspects, the detected value of the current transformer is A / D converted, and the data is processed by a data processing device such as a computer. The correction operation is performed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on preferred embodiments shown in the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of a PWM current detection device according to the present invention, together with a circuit to be detected to which the present invention is applied. In the figure, an energizing element series circuit in which energizing elements 11P and 11n, which are transistors that can be turned on and off and allow a current to flow through only one of them and a switching element represented by an IGBT, are connected in series is shown. Contains. These energizing elements 11P and 11n are connected in anti-parallel to reflux elements 12p and 12n, each of which is a one-way energizing element typified by a diode capable of flowing a current to only one of them. Also,
The DC power supplies 14p and 14n are connected in series, the positive electrode is connected to the positive terminal of the energizing element series circuit, and the negative electrode is connected to the negative terminal of the energizing element series circuit. Further, an inductive load 13 is connected between the interconnection point of the biasing elements 11P and 11n and the interconnection point of the DC power supplies 14p and 14n. These constitute the circuit 1 to be detected.

In order to detect a current flowing through the load 13 in the circuit 1 to be detected, a current transformer 2 generally called ACCT is provided, and an output terminal of the current transformer 2 has a voltage value corresponding to the current value. The sampling means 3a is connected to the sampling means 3a, and the sampling means 3a is connected to a delay sampling means 3b for storing the output of the sampling means 3a and delaying the output for a predetermined time and outputting the result. Also, sampling means 3
There is provided a difference output means 4 for calculating a difference between the output of a and the output of the delay sampling means 3b. The difference output means 4 outputs a signal corresponding to the rate of change of the current flowing through the load 13. The difference output means 4 is connected to an absolute value comparison means 5 for detecting that the output, that is, the rate of change of the load current has become substantially zero.
The output terminal of the current transformer 2 is connected to a sample-and-hold means 6 for holding the value when a signal is output from the absolute value comparing means 5, and one input terminal (+) is connected to the The input terminal (-) is connected to the output terminal of the sampler 2 and the other input terminal (-) is connected to the output terminal of the sample-and-hold means 6, and has an analog operation means 7 having the function of an adder.

Further, when a signal is output from the absolute value comparing means 5, an all driving signal output means 8 for outputting all driving signals, which will be described in detail later, is provided. Is provided as one input and the output signal of all drive signal output means 8 as the other input.
In accordance with the output signal of the element selecting means 9, the driving means 10 controls on and off of the biasing elements 11P and 11n.

Regarding the present embodiment configured as described above, first, full drive PWM control and half drive PWM control related to the present invention will be described, and then the operation thereof will be described.

FIG. 5A shows the state of the current flowing to the load 13 of the circuit 1 to be detected shown in FIG. 1, and is indicated by the solid arrow by the on / off control of the biasing elements 11P and 11n. The current flows in the direction, or the current flows in the direction indicated by the dashed arrow. Therefore, the biasing elements 11P and 1
By performing PWM control on 1n, a sine-wave current can flow through the load 13. FIG. 5B shows a current waveform near a zero-crossing point where the fundamental component changes from positive to negative when the energizing elements 11P and 11n are subjected to PWM control, and states of ON and OFF of the energizing elements 11P and 11n. FIG.

Here, the urging element 11P is turned on,
When the biasing element 11n is turned off, the current in the direction indicated by the solid arrow increases, and conversely, when the biasing element 11P is turned off and the biasing element 11n is turned on, the current is indicated by the broken arrow. The current in the direction increases. In the following description, an increase in current in the direction indicated by the solid arrow is called an increase in load current,
An increase in the directional current indicated by the dashed arrow is referred to as a decrease in the load current. Therefore, the fundamental wave component reaches a peak value in the positive direction or a peak value in the negative direction by repeatedly increasing and decreasing the load current.

Now, in the section a in which the biasing element 11P is turned off near the zero-cross point of the fundamental wave component, a current flows through the reflux element 12n so as to retain the current that has been flowing through the biasing element 11P immediately before. Therefore, the load current gradually decreases. Subsequently, if the energizing element 11P is turned on in a section b before the load current reaches zero, the load current gradually increases. Next, in the section c after the energizing element 11P is turned off and the energizing element 11n is turned on at the same time, the current in the direction for maintaining the immediately preceding load current flows through the reflux element 12n, and the load current reaches zero. I do. Thereafter, in section d, a current flows through the biasing element 11n, and the load current continues to decrease. That is, the boundary between the section c and the section d is the zero cross point of the load current.

Next, assuming that the biasing element 11P is turned on and the biasing element 11n is turned off,
In section e, the load current flows through the biasing element 11P, during which the load current gradually increases from a negative value toward zero, and also in section f past the zero point, the load current gradually increases. That is, the boundary between the section e and the section f is the zero cross point of the load current. Such biasing elements 11p connected in series,
In this specification, the control of driving the biasing element so that 11n is complementary, that is, when one element is ON, the other element is OFF, and when one element is OFF, the other is ON,
This is referred to as WM control.

FIG. 6 is an explanatory diagram for explaining the half-drive PWM control. FIG. 6A shows the state of the current flowing through the load 13 of the detected circuit 1 shown in FIG. Therefore, a current flows in a direction indicated by a solid-line arrow or a current flows in a direction indicated by a dashed-line arrow by ON / OFF control of the urging elements 11P and 11n. Therefore, a sinusoidal current can be supplied to the load 13 by performing PWM control on the urging elements 11P and 11n. In the figure, (b) shows the current waveform near the zero-cross point where the fundamental component changes from positive to negative when the energizing elements 11P and 11n are subjected to PWM control, and the on / off state of the energizing elements 11P and 11n. FIG.

As described above, when the biasing element 11P is turned on and the biasing element 11n is turned off, the current in the direction indicated by the solid arrow increases, and conversely, the biasing element 11P is turned off. When the biasing element 11n is turned on, the current in the direction indicated by the broken arrow increases. Therefore, the fundamental wave component reaches a peak value in the positive direction or a peak value in the negative direction by repeatedly increasing and decreasing the load current.

Now, in the section a 'where the energizing element 11P is off near the zero-cross point of the fundamental wave component, the current flowing through the recirculating element 12n is held so as to retain the current flowing in the energizing element 11P immediately before. , The load current gradually decreases. Subsequently, if the energizing element 11P is turned on in a section b 'before the load current reaches zero, the load current gradually increases. Next, assuming that the biasing element 11n is kept in the off state in the sections c 'and d' after the biasing element 11P is turned off, in the section c ', a current flows through the reflux element 12n and gradually decreases. Subsequently, if the biasing element 11n is held in the off state, the load current detects this point as a zero-cross point, and in the subsequent section e ', the control shifts to the above-described full drive PWM control to turn the biasing element 11n on. , The load current rapidly decreases from zero, and then, if the biasing element 11P is turned on and the biasing element 11n is turned off, the load current increases toward zero in the section f ′. , Further increases from zero in the section g ′. That is, the boundary between the section f 'and the section g' is the zero cross point of the load current.

Next, assuming that the urging element 11P is turned off and the urging element 11n is turned on,
In section h ', the load current flows through the freewheeling element 12n, during which time it gradually decreases from a positive value toward zero, and in section i' past the zero point, the load current flows through the energizing element 11n and , Gradually decrease. That is, the boundary between the section h 'and the section i' is the zero cross point of the load current. Thereafter, if the energizing element 11P is turned on and the energizing element 11n is turned off, the load current increases in the section j '. As described above, the energizing element 11n includes the energizing element 11P in a state in which the energizing element 11P is kept in the OFF state and the current for maintaining the current value flows through the recirculating element 12n. In this specification, the control for keeping the biasing element 11n in the off state in the section in which is to be turned on is referred to as half-drive PWM control. That is, even when the high-voltage-side energizing element 11p is OFF in the section in which the positive-side current flows, the low-voltage-side energizing element 11p is kept OFF, and conversely, the section in which the negative-side current flows. In the above, half-drive PWM control is a control for keeping the high-voltage-side energizing element 11p OFF even when the low-voltage-side energizing element 11p is OFF.

As described above, in the vicinity of the zero cross point of the fundamental wave current component, the return element 12n or 1
When the biasing element 11n or 12p connected in anti-parallel to 2p is kept in the off state, the current becomes zero and the current change rate becomes substantially zero. Therefore, when the absolute value of the current change rate becomes substantially zero, it can be said that the actual load current is zero.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be described with reference to the time chart of FIG. 2 and also to FIG. I do. The detected circuit 1 in FIG. 1 shows, for example, a driving system corresponding to one winding of a three-phase DC brushless motor, and the element selecting means 9 outputs a positive side driving signal f shown in FIG. When the negative drive signal g shown in FIG. 2E is applied to the drive means 10, the drive means 10
By controlling the 1P and 11n to be turned on and off, a well-known PWM current having a sine wave of a fundamental component flows through the load 13. As described above, in the motor that drives the compressor, when the load torque changes periodically, the DC component is superimposed on the winding current in accordance with the change. However, even if the current flowing through the load 13 is detected by the current transformer 2, the DC component cannot be detected. In the section T1, half-drive PWM control is performed.

That is, as shown in FIG. 2A, the load 13 actually supplies the current of the sum of the positive DC component d and the AC component b (the lower PWM current waveform in the figure). Even if it is flowing, the current transformer 2 only obtains a signal corresponding to the AC component b. The portion where the DC component d slightly changes in a step-like manner indicates, as will be described later, an error that the previously detected DC component has deviated from the actual value, for example, at the time when a half cycle has elapsed. I have.

Next, when the above-described half-drive PWM control is continued near the zero-cross point of the fundamental wave component of the current, the absolute value of the rate of change of the current becomes substantially zero. Section T2 in FIG. 2A shows this state.

In order to detect that the absolute value of the rate of change of the current is substantially zero, the sampling means 3a samples the output of the current transformer 2 at a shorter cycle than the carrier signal, and the delay sampling means 3b The output is delayed at least by the sampling period, the difference output means 4 compares the two sampled values, and based on the comparison result, the absolute value comparison means 5 determines that the absolute value of the current change rate is substantially zero. And outputs a zero current detection signal c as shown in FIG. At this time, the sample and hold means 6 holds the value of the output signal b of the current transformer 2. This DC component is thereafter applied to the negative (-) terminal of the analog operation means 7 until the zero current detection signal c is output. Therefore, a detection signal h on which the positive DC component is superimposed is obtained from the analog operation means 7.

On the other hand, when the zero current detection signal c shown in FIG. 2 (b) is output, the entire drive signal output means 8 operates for a predetermined period, that is, a period during which the load current may have a zero crossing tolerance due to the increase or decrease of the load current. Only outputs the entire drive signal e,
In response to this, the element selecting means 9 determines the internal polarity and the total drive signal e.
As a result, the positive drive signal f and the negative drive signal g are output, and the load current of the detected circuit 1 starts flowing in the opposite direction. A section T3 in FIG. 2A shows a full drive PWM control section. This full-drive PWM control section is set to a period of, for example, 30 degrees, and when it exceeds that, half-drive PWM control is performed again to detect the next zero-cross point.

FIG. 3 is an enlarged view of a section slightly after 380 ms shown in FIG. 2, and since a half cycle has elapsed since the previous detection, the DC component is shifted from the correction value by ΔI. Even if there is, the error is also corrected. That is, even if the output signal h of the analog operation means 7 is smaller than the actual current value a by ΔI in accordance with the error of ΔI of the DC component, at the stage when the zero current detection signal c is output. The corrected detection signal h corresponding to the true current a flowing through the load 13 is obtained. Thus, the zero-cross point t1 calculated based on the DC current error ΔI is corrected to t2.

Thus, according to this embodiment, the instantaneous value of the AC current waveform on which the DC component is superimposed can be obtained by a current transformer generally used without using a DC magnetic flux detecting means such as a Hall element. Can be accurately estimated and calculated from the output waveform.

Further, the drive current for driving the load can be kept low, and the influence on the current waveform can be kept to a minimum. To summarize the above, the full-drive PWM control is performed in the section from the zero-cross detection to 30 degrees, the half-drive PWM control is performed after 30 degrees, and the control that becomes the full-drive PWM control when the zero cross is detected again is repeated. . Since the direction of the current to be flown is reversed by the zero cross, the biasing element maintained in the OFF state in the half-drive PWM control is switched every time the zero cross occurs.

In the above-described embodiment, the all drive signal output means 8 is provided so that all drive signals are output immediately after generation of the zero current detection signal.
Although switching to the WM control is performed, if the entire drive signal output means 8 is removed, there may be a plurality of zero current sections near the zero crossing point of the fundamental wave component. Although it is not desirable as a waveform,
The offset current can be detected in the same manner as in the above embodiment. In the present embodiment, 180
In each half-wave section of the degree, the 30-degree section from the detection of the zero-cross is set to the full drive PWM control, and the remaining 150-degree section is set to the half-drive PWM control. , The half-drive PWM control may be performed, and in other periods, the full-drive PWM control may be continued.

Furthermore, even in a current transformer having sufficiently improved low-frequency characteristics, a slight phase shift (generally leading) is included in the detected waveform in addition to the offset current. This effect appears as a shift in the detected value of the offset current due to the phase at the time of detecting the zero cross point. That is, among the DC components shown in FIG. 2A, the sign of the error ΔI differs between the case where the fundamental wave component changes from positive to negative and the case where the fundamental wave component changes from negative to positive. Accordingly, if the average value of the error ΔI when the fundamental wave component changes from positive to negative and the error ΔI when the fundamental wave component changes from negative to positive is set as the offset current, the discontinuity of the current detection waveform is improved. .

Further, the fluctuation of the offset current is sufficiently slow as compared with the carrier frequency (drive frequency), and higher accuracy can be obtained by averaging the detected values for a plurality of cycles to obtain the offset current value. May be In this case, not only the average value of the two detected values, but also a moving average value of more detected values can be adopted.

Further, when the AC frequency is high, the half-drive P
The effect of the delay of the rising waveform of the current due to sampling on the WM waveform has a large effect on the current detection waveform and vector control. Therefore, if the offset current is not detected every cycle but detected at intervals of the number of rotations or time, the offset current can be detected while suppressing the influence on the operation even at the time of high-speed operation of the motor.

By applying the PWM current detection device according to the above embodiment to vector control in which the load torque changes depending on the rotational position and the average value of the current differs depending on the phase of the motor, like a compressor drive motor. , Optimal control can be performed.

In the embodiment shown in FIG. 1, the sampling means 3a, the delay sampling means 3b, the difference output means 4, the absolute value comparing means 5, the sample and hold means 6,
Each function of the analog operation means 7 and the entire drive signal output means 8 can be provided in a digital signal processing device such as a microprocessor.

FIG. 4 shows an application example of the embodiment shown in FIG. In FIG. 1, a converter circuit 22 is connected to an AC power supply 21.
Are connected, whereby AC is converted to DC. A DC output terminal of the converter circuit 22 is connected with six transistors as energizing elements in a bridge connection, and a DC input terminal of an inverter circuit 23 in which diodes as recirculation elements are connected in anti-parallel to these transistors is connected. ing. A permanent magnet motor 24 is connected to an AC output terminal of the inverter circuit 23. Current transformers 25U and 25W are provided to detect the U-phase and W-phase currents of the connection path of the permanent magnet motor 24.
These current transformers 25U and 25W are connected to current correction means 26U and 26W for detecting the current of each phase in consideration of the offset current.

The current correction means 26U and 26W are respectively composed of the sampling means 3a, the delay sampling means 3b, the difference output means 4, the absolute value comparison means 5,
A sample and hold unit 6 and an analog operation unit 7 are provided. The three-phase current calculation means 27 is connected to the current correction means 26U and 26W. The three-phase current calculation means 27 calculates the V-phase current using the fact that the sum of the currents of the U, V, and W phases is zero, and calculates the vector calculation means as the current detection values of the U, V, and W phases. Add to 28. As is well known, the vector calculation means 28 obtains respective command values of the torque component current, the magnetic flux component current, and the slip frequency, and then outputs three-phase current commands by treating them with vector orthogonal components. The full-drive / half-drive calculating means 29 generates on / off signals for the transistors constituting the inverter circuit 23 based on the three-phase current command, and executes the full-drive PWM control and the half-drive PWM control described above. Then, a part of the ON signal of the transistor is converted into an OFF signal and applied to the drive circuit 30. The drive circuit 30 controls the transistor in accordance with the on / off signal obtained by converting a part of the on signal into an off signal.

By using the control device configured as described above, the vector control of the permanent magnet motor 24 that drives the compressor such as an air conditioner can be performed with high accuracy.

As is apparent from the above description, according to the present invention, the DC component is superimposed by the current transformer generally used without using the DC magnetic flux detecting means such as the Hall element. The instantaneous value of the AC current waveform
PW accurately estimated and calculated from the output waveform
An M current detection device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a PWM current detecting device according to the present invention, together with a circuit to be detected to which the present invention is applied.

FIG. 2 is a time chart showing a voltage or current waveform of each unit for explaining the operation of the embodiment shown in FIG. 1;

FIG. 3 is a time chart showing an enlarged part of a section shown in FIG. 2 to explain the operation of the embodiment shown in FIG. 1;

FIG. 4 is a block diagram showing a configuration of a control circuit in which the PWM current detection device according to the present invention is applied to a control device of a permanent magnet motor.

FIG. 5 is an explanatory diagram for explaining full drive PWM control related to the present invention.

FIG. 6 is an explanatory diagram for explaining half-drive PWM control related to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Circuit to be detected 2 Current transformer 3a Sampling means 3b Delay sampling means 4 Difference output means 5 Absolute value comparison means 6 Sample hold means 7 Analog operation means 8 All drive signal output means 9 Element selection means 11P, 11n Energizing element 12p , 12n Reflux element 13 Load 14p, 14n DC power supply DC power supply 25U, 25W Current transformer 26U, 26W Current correction means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G035 AA00 AB07 AB08 AC02 AC13 AC24 AD19 AD48 5H007 AA07 BB06 CA01 CB02 CB05 CC23 DA05 DB13 DC02 EA04 5H560 AA02 BB04 BB12 DC12 EB01 EC01 EC10 RR03 SS01 TT15 UA03 XA02 XA02 CC05 DD02 DD07 EE01 EE14 GG04 HA04 HB01 JJ03 JJ08 LL22

Claims (7)

[Claims] An energizing element series circuit in which energizing elements capable of one-way energization by on / off control are connected in series, and an energizing element capable of unidirectional energization and antiparallel connected to the energizing elements, respectively. And a return element connected to the power supply unit, a positive terminal of the DC power supply is connected to a positive terminal of the energizing element series circuit, a negative terminal of the DC power supply is connected to a negative terminal, and the energizing elements are interconnected. PWM current detection for connecting one end of a load to a point, connecting the other end of the load to a predetermined point regarded as a voltage range of the DC power supply, and detecting a current flowing to the load when the energizing element is PWM-controlled. In the device, a current transformer that detects only an AC component of the current flowing through the load in a DC-insulated state, and a predetermined section including a section in which current flows through the freewheel element due to the inductive action of the load. Anti-parallel connected to the reflux element Half driving PWM for holding the biasing element off state
Execute the control, the absolute value of the time rate of change of the current transformer in the holding section of the detection value is considered to be substantially zero, assuming the zero level of the current flowing to the load, the detection value of the current transformer And a detection value correcting means for correcting and outputting the detected value. 2. When the biasing element is held in an off state after detecting a detection value in which the absolute value of the time rate of change of the current transformer is substantially zero in the holding section, the current flows to the load. The section in which the current is predicted to be zero enables the energizing element connected in anti-parallel to the freewheel element to be in the on state even in a predetermined section including the section in which the current flows through the freewheel element. The PWM current detection device according to claim 1, wherein full-drive PWM control is performed. 3. A detection value when a fundamental component of a current flowing through the load changes from positive to negative, among detection values for which an absolute value of a time rate of change of the current transformer is considered to be substantially zero, From the detected value when it changes to positive, calculate the average value, and calculate the obtained value when the fundamental component of the current flowing through the load changes from positive to negative, and from negative to positive. The PWM current detection device according to claim 1 or 2, wherein the current is set to a zero level when the current changes. 4. An apparatus according to claim 1, wherein an average value of a plurality of latest detection values among the detection values for which the absolute value of the time change rate of the current transformer is considered to be substantially zero is used as the correction value. The PWM current detection device according to any one of claims 1 to 3. 5. The current transformer according to claim 1, wherein the detected value of the current transformer is corrected at a plurality of cycle intervals of a fundamental wave component of the current flowing through the load or at a time interval corresponding to a plurality of cycles. The PWM current detection device according to any one of the preceding claims. 6. The PWM current detection according to claim 1, wherein an output of said detection value correction means is used as input information for vector control of a three-phase DC brushless motor. apparatus. 7. The PWM according to claim 1, wherein a detection value of the current transformer is A / D converted, and a correction operation is executed by a data processing device such as a computer. Current detector.