JP2775572B2 - Current control method of self-excited voltage type AC / DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control system for a self-excited voltage type AC / DC converter, and can be applied to output means of an audio amplifier as an application field.

[0002]

2. Description of the Related Art A self-excited voltage type AC / DC converter (hereinafter referred to as PC)
There are two types of current control methods known as S), namely, a triangular wave comparison PWM method (FIG. 4A) and a hysteresis comparator method (FIG. 4B). The triangular wave comparison PWM method is a method of obtaining a PWM signal by feeding back the instantaneous value _ic of the compensation current, amplifying it against a command value _ic *, and comparing the amplified value with a triangular wave carrier. On the other hand, in the hysteresis comparator system, the instantaneous value _ic of the compensation current is fed back and matched with the command value _ic * in the same manner as in the above-described system, but thereafter, a PWM signal is obtained via the hysteresis comparator. is there. In each of the above conventional examples, the PWM signal is
This is performed by on / off control by gate control of a bridge configuration of the semiconductor switching element.

[0003]

Among the above-mentioned conventional methods, the former has a problem that a control deviation occurs with respect to a randomly changing current waveform, and the latter has a problem that it is difficult to balance a current ripple value and a gate frequency. And there is control complexity. The present invention has been made in view of the above circumstances, and not only can an arbitrary function be used as a target function of an AC current, but also a self-excited type that can use an arbitrary value as a target tracking error width of an AC current. It is an object of the present invention to provide a current control method for a voltage type AC / DC converter.

[0004]

According to a first aspect of the present invention, there is provided a current control system for a self-excited voltage type AC / DC converter, wherein a DC voltage source is connected to a single-phase AC system via the self-excited voltage type AC / DC converter. In the AC / DC converter, a first A / D conversion circuit for sampling the AC current at the interconnection point and performing analog-to-digital conversion, and a second A / D converter for sampling an arbitrary target function and performing analog-to-digital conversion A / D conversion circuit, a third A / D conversion circuit that samples a target tracking error signal that is a predetermined margin of change of the target function and performs analog-to-digital conversion, and the first and second conversion circuits. A subtractor that receives an output of each A / D conversion circuit as an input, detects a difference (error signal) between the AC current at the interconnection point and a target function, and outputs the difference (error signal) at regular sampling periods; Subtractor output And a comparator which receives as input the output of the third A / D conversion circuit and determines whether or not the error signal is within the target tracking error signal, and a gate command for each switching element of the AC / DC converter based on the comparison result. And an arithmetic circuit having means for generating only the error signal.When the error signal deviates from a set range by the target tracking error signal, the switching mode of the AC / DC converter is changed to a target function. It is to follow. The current control method according to the second aspect uses a switching mode other than the circulation mode as a switching operation of the AC / DC converter. According to a third aspect of the present invention, in the AC / DC converter in which a DC voltage source is connected to a three-phase AC system via a self-excited voltage type AC / DC converter, an arbitrary two-phase AC current at the interconnection point is provided. First and second A / D conversion circuits for sampling and analog-to-digital conversion, respectively, and third and fourth A / D conversion circuits for sampling arbitrary target functions corresponding to the respective current phases and performing analog-to-digital conversion.
An A / D conversion circuit, a fifth A / D conversion circuit for performing analog-to-digital conversion of a target tracking error signal which is a preset margin of change of the target function, and the first and second A / D conversion circuits.
The first three-phase to two-phase conversion circuit which receives the output of each A / D conversion circuit as an input and outputs an α-phase current and a β-phase current, and the output of each of the third and fourth A / D conversion circuits A second three-phase-to-two-phase conversion circuit that receives as input each of the α-phase and β-phase target functions, and the α-phase currents and the respective ones from the first and second three-phase to two-phase conversion circuits. a first and a second subtractor for respectively inputting a β-phase current and outputting the difference (error signal) at each constant sampling period, and two errors from the first and the second subtractors. A comparator which receives a signal and a target tracking error signal from the fifth A / D conversion circuit, and determines whether each of the error signals is within the target tracking error signal, and an AC / DC converter based on the comparison result And an arithmetic circuit having means for generating a gate command for each switching element based on only the error signal. , And the when said error signal is outside the set range by the target tracking error signal, it is intended to follow the target function by changing the switching mode of the AC-DC converter.

[0005]

According to the current control method of the self-excited voltage type AC / DC changer according to the first aspect of the present invention, the AC current at the interconnection point is detected and compared with a preset reference value. If the comparison result deviates below the reference value, the switching mode in the upward direction is selected, and if the comparison result deviates upward, the switching mode in the downward direction is selected. These raising and lowering operations are repeatedly performed at each current sampling time so as to follow the target value. According to a second aspect of the present invention, the on / off operation is performed by excluding the recirculation mode from the switching modes. In the current control method according to the third aspect, since the AC system is a three-phase system, control is performed using the fact that the degree of freedom is two. That is, an interconnection point current of any two of the three phases is detected, and this is converted from three-phase to two-phase to obtain α.
Phase and β phase currents are obtained. On the other hand, the two-phase currents of the reference value are also converted from three-phase to two-phase, respectively, so that the α-phase and β-phase
Obtain phase current. Then, the reference and the detected value are compared for each of the same phase currents, and according to the comparison result, for example, each switching mode in the upward direction when deviating downward, and in the downward direction when deviating upward. Select .

[0006]

An embodiment will be described below with reference to the drawings. FIG.
FIG. 1 is a configuration diagram of an embodiment for explaining a current control method according to the present invention, showing a case of a single-phase circuit. In FIG. 1, the left side from the point A indicates the AC system side, e (t) is an AC voltage,
L _S is the inductance of the system, and i (t) is the AC current value at the interconnection point. Point B from the right side indicates the outside of the apparatus, E _B is a DC voltage source (secondary voltage). Note that L _P is a connection inductance in the PCS, i _B (t) is a current value of a DC voltage source (including a capacitor), and v (t) is a voltage behind L _{P in} the PCS. U, X, V, and Y are self-extinguishing type main elements that connect V and Y connected in series to U and X connected in series, and connect each of the AC system side via points a and b. Connect to terminal. Then, reverse conducting diodes D _U , D _X , D _V , and D _Y are connected in parallel to each of the main elements. An AC current value i (t) at the interconnection point is taken out from the point a side of the main circuit and input to the subtractor 2 via the A / D conversion circuit 1, while the target function value j
(t) is input to the subtractor 2 via the A / D conversion circuit 3.
Reference numeral 4 denotes a comparator, which outputs an error signal from the subtractor 2 and A
And a target follow-up error signal j (e) via the / D conversion circuit 5 and output the comparison result to the gates of the main elements U, V, X, Y via the dead time circuit 6. ing.
Note that the target value function j (t) is an arbitrary function.

In the main circuit of FIG. 1, the alternating current i (t) at the interconnection point satisfies the following differential equation at an arbitrary time t.

(Equation 1) Then, the increase or decrease of the current at the interconnection point can be freely controlled by turning on / off the main element. The switching modes used in this control equation can be three types shown in Table 1 below.

[Table 1]

Next, the operation will be described. In FIG. 1, an AC current i (t) at an interconnection point of a main circuit is detected, converted into a digital quantity via an A / D conversion circuit 1, and introduced into a subtractor 2. On the other hand, an arbitrary target function j (t) is also converted into a digital quantity via the A / D conversion circuit 3 and is introduced into the subtractor 2. In the subtractor 2, a difference between the AC current i (t) and the target function is detected, and this difference (error signal) is calculated by the arithmetic circuit 4.
Is input to Further, a predetermined target tracking error signal j (e) is input to the arithmetic circuit 4. Here, the target tracking error signal is a margin limit width set as the target function j (t) ± j (e).

In the arithmetic circuit 4, it is determined whether or not the error signal is within the target tracking error signal. If the error signal is outside the lower limit (-j (e)), the AC current i (t) at the interconnection point is determined. Is increased, and a gate signal for decreasing the AC current i (t) is output if the value exceeds the upper limit (+ j (e)). The switching mode in that case is selected from Table 1. That is, mode 1 is an up operation, mode 3 is a down operation, and mode 2 is a recirculation mode.

Next, the contents of the calculation will be described in detail with reference to FIG. FIG.
Indicates the AC current (A) on the vertical axis and the time (s) on the horizontal axis. In the figure, j (t) is an arbitrary target function, and has a target tracking error width j (t) + j (e) and a width of j (t) -j (e) around this target function. now,
Consider the case where alternating current I _n at sampling time t _n has been detected. In this case, the target function is the j (t _n), the difference becomes j (t _n) -I _n. That I _n than the target function is a small. Here, the processing time of the measurement control circuit required after the data is collected until the next switching mode is determined is T _c (s). Incidentally, the T _c ≦ T _s,
Tc is called a control delay time.

Accordingly sampling the alternating current at the sampling time t _n, performs a positive direction of the control after the control delay time T _c. At the next sampling time t _{n + 1} , the sampled AC current is I _{n + 1} , but the target function is j (t _{n + 1} ), and the difference is still smaller than the target function. Therefore, control in the forward direction is further performed. Next, at the sampling time t _{n + 2} , the detected current value becomes I _{n + 2} , which is larger than the target function j (t _{n + 2} ). Therefore, negative direction control is performed, and the above processing is repeated at the next sampling time. The mode at t = t _n + T _c is t = t _n-1 +
DC short-circuit (arm short-circuit) when the mode is different from _Tc mode
To prevent this, first, mode 0 (a mode in which all elements are OFF and not shown in Table 1) is inserted by T _d (s) (entrance delay time). _Td is determined by the turn-off time of the main element. By repeating the above process,
It will gradually approach the objective function. It should be noted that T _c <T _s . The target tracking error width as a calculated value was j (t) ± j (e).

(Equation 2) It was found by calculating back from the calculated value. The actual width is indicated by a dotted line. According to the above-described embodiment, current control is possible by detecting only the relationship whether the actual current value is larger or smaller than the target function.

Another embodiment of the switching mode is shown in Table 2.

[Table 2] The above processing is also possible in the switching mode. In this embodiment, the circulation mode is omitted.
In this case, based on the error I _n -j (t _n) between the actual AC current I _n and the target current value j (t _n), the switching command at time t _n + T _c which was defined as follows is there. I
_{If n−} j (t _n ) <0, mode 1, I _n −j (t _n )
If> 0, set to mode 3. Incidentally, the mode at t = t _n + T _c, in order to prevent the t = t _n-1 + modes with different time DC short circuit in at T _c (arm short circuit), the first mode 0 (all elements are OFF mode (Not shown in Table 2) is inserted by T _d (s) (entrance delay time). T
_d is determined by the turn-off time of the main element. The present invention can also be achieved by the above embodiments.

FIG. 3 is a block diagram of another embodiment of the present invention, in which the main circuit is a three-phase bridge. The difference in the configuration is that the self-extinguishing main element for the three-phase bridge is W
And Z are connected in parallel to a conventional configuration. From the points a, b, and c, connection was made to each of the three terminals at the interconnection point. The newly added main elements W and Z
Are connected in parallel with the reverse conducting diodes D _W and D _Z as described above. In the AC system, E _A
Is the effective value of the system-side three-phase AC line voltage, i _a (t), i
_{b (t), i c (} t) is the interconnection point a, b, c phase alternating current instantaneous _{value, v 1 (t), v} 2 (t) behind the voltage between L _P in PCS (b-a ) And (bc). And, in the combination of switching of each main element, the simultaneous U, X, V, Y, and W, Z are DC short-circuits (arm short-circuits). Note that a specific combination of switching is omitted because it is complicated by 162 cases.

Next, since the conversion device viewed from the interconnection point is a three-terminal element, the expression (4) is satisfied at an arbitrary time t.

Equation 3 Since the degree of freedom in _{i a (t) + i b} (t) + i c (t) = 0 ............ (4) where the alternating current is 2, a i _a and i _c in this embodiment Free. In short, in the case of the AC current waveform control of the three-phase bridge configuration, only two phases of the three-phase current are subjected to the waveform control, and the current value of the remaining one phase is instantaneously obtained by the equation (4). Will be determined by

In the circuit configuration of FIG. 3, any time t ₁
Then, the following simultaneous differential equation of equation (5) holds.

(Equation 4)

Since the two phases cannot be independently increased or decreased in this state, α and β coordinate conversion is performed (α and β conversion is performed in July, 1985, Transactions of the Institute of Electrical Engineers of Japan, paper 60-B65,
(Described in equation (2)).

(Equation 5) The functions i _α (t) and i _β (t) according to Eq.
Phase current and β phase current. Although the detailed description is omitted here, the basic equation of the three-phase bridge circuit of the above-mentioned equation (6) is rewritten with respect to the α-phase component i _α (t) and the β-phase component i _β (t). become that way.

[0017]

(Equation 6) _{That, i a (t), i} b (t), 3 -phase with respect to i _c (t) → 2
The phase-converted i _α (t) and i _β (t) satisfy the above equation (8). In this case, each phase is made non-interfering. Therefore the above
In the same way as in equation (3),

(Equation 7) If, the increase or decrease of the current at the interconnection point can be controlled by turning on / off the main element.

The switching modes used in this control equation are as shown in Table 3.

[Table 3]

The specific structure is the same as in FIG. 3, was chosen as the freedom a phase current i _a, 3-phase → 2 phase c-phase current i _c through the respective A / D converter circuit 11,11-1 The conversion circuit 16 introduces the α-phase current to the subtractor 12 and the β-phase current to the
Introduce to 12-1. On the other hand, any objective function j _a, a j _c A
Three-phase to two-phase conversion circuit 16-1 via / D conversion circuits 13 and 13-1
Then, the α-phase current is introduced into the subtractor 12 and the β-phase current is introduced into the subtractor 12-1. Then, the outputs of the respective subtracters are introduced into the arithmetic circuit 14, and the target tracking error signal j (e) is also introduced, and each gate signal as an arithmetic output is output to control the main element. The control method is the same as that described with reference to FIG.

Table 4 shows which switching mode (Table 3) is selected for control. That is, any time t =
error i _α (t _n) -j of α-phase current in the t _n
α (t _n ) and β phase current errors i _β (t _n ) −j _β (t
Table 4 defines the switching mode at time t = t _n + T _C according to the value of _n ). Note that time t = t _n
When the switching mode at + T _C is different from the switching mode at t = t _n-1 + T _C , mode _{1 is first} switched by T _d [s] (entrance delay time) to prevent a DC short circuit. insert. The value of _Td is determined by the turn-off time of the main element. As described above, control can be performed also in the case of three phases.

[Table 4]

[0021]

As described above, according to the present invention, not only an arbitrary function can be used as a target function of an AC current, but also an arbitrary value can be used as a target tracking error width of an AC current. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment for describing a current control method of a self-excited voltage type AC / DC converter according to the present invention.

FIG. 2 is a waveform chart for explaining the operation of FIG. 1;

FIG. 3 is a configuration diagram of another embodiment.

FIG. 4 is a diagram illustrating a conventional device.

[Explanation of symbols]

 1,3,5,11,11-1,13,13-1,15 A / D conversion circuit 2,12,12-1 Subtractor 4,14 Operation circuit 16,16-1 3 phase → 2 phase conversion circuit

Claims (3)

(57) [Claims] A DC voltage source is a self-excited voltage-type AC / DC converter.
AC-DC converter connected to a single-phase AC system via
Te, analog samples the alternating current of the interconnection point
A first A / D conversion circuit for digital conversion, and an optional
Analog to digital conversion by sampling target function
A second A / D conversion circuit, and a predetermined target
The target tracking error signal, which is the margin of function change, is sampled.
A / D conversion for analog-to-digital conversion
Conversion circuit, and outputs of the first and second A / D conversion circuits.
The difference between the AC current at the interconnection point and the target function
Signal) and the difference (error signal)
A subtractor that outputs a signal every period;
/ D conversion circuit and the error signal
A comparator for determining whether the signal is within the slave error signal,
According to the comparison result, each switching element of the AC / DC converter is
For generating a gate command based on only the error signal
A current control method for a self-excited voltage-type AC / DC converter , comprising: an arithmetic circuit having: 2. The current control method for a self-excited voltage-type AC / DC converter according to claim 1, wherein the switching operation of the AC / DC converter uses a switching mode other than the circulation mode. 3. A self-excited voltage type AC / DC converter having a DC voltage source.
AC / DC converter connected to a three-phase AC system via
Te, sampling the alternating current of any two phases of the interconnection point
1st and 2nd A for analog-to-digital conversion
/ D conversion circuit and an arbitrary target function corresponding to each current phase.
Number that converts the analog-to-digital conversion
(3) a fourth A / D conversion circuit and the preset target
The target tracking error signal, which is the margin of function change, is analog
A fifth A / D conversion circuit for performing digital conversion;
1, the output of each of the second A / D conversion circuits is used as an input and the α-phase current
And a first three-phase to two-phase conversion circuit that outputs a β-phase current and
The outputs of the third and fourth A / D conversion circuits are
The second three phases that output the α-phase and β-phase target functions → 2
A phase conversion circuit and the first and second three-phase to two-phase conversion circuits
Input each α-phase current and each β-phase current from
The difference (error signal) is output at every fixed sampling period
First and second subtractors, and the first and second subtractors
From the second error signal and the fifth A / D conversion circuit.
Of the target tracking error signal, and each of the error signals
A comparator for determining whether the signal is within the slave error signal,
According to the comparison result, each switching element of the AC / DC converter is
For generating a gate command based on only the error signal
A current control method for a self-excited voltage-type AC / DC converter , comprising: an arithmetic circuit having: