JPS5858902B2 - DC chopper control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC chopper control force type, and its purpose is to more accurately suppress negative conductance vibrations occurring in an LC filter on the power supply side without increasing control errors in constant current control of a load. The goal is to provide a DC chopper control force type that can be used.

Choppers, especially silice choppers, are used for intermittent control due to their fast switching action and long life.However, if the distance between the power supply and the load is long, there is an inductive disturbance caused by the pulse current during intermittent operation, and the LC on the power supply side is generally used. Filters are considered essential.

In the case of constant current control of the load (based on the instantaneous current value),
As an example of this, electric cars are often cited in the literature, but it is well known that if the control is maintained even when the power supply fluctuates, negative conductance will occur in the LC filter, causing large-amplitude vibrations on the power supply side. be.

The first method was to detect the instantaneous value of the current of the load, which is a motor, and to control the current to keep the current pull width within a predetermined range. This will be explained based on Figure a.

In the same figure a, Es is a DC power supply, LF and CF are inductances and capacitors constituting the above filter, and La
, Ra is the inductance and resistance of the load such as a motor, A is the chopper, and B is the comparator. The instantaneous value ia of the load current is compared with the set current value Ir by comparator B, and the comparison output turns chopper A on and off. controlled.

That is, when it is desired to supply a current value of Ir to the load, if the load current ia exceeds Ir by △ia, the chopper is turned off and Ir
If △ia decreases, the chopper is turned on and its load current i
a pulsates by Δ±ia around Ir, but on average Ir
constant current control is maintained.

Here, the comparator B is understood to have a hysteresis characteristic that determines the fluctuation width of its member △ia, and if the hysteresis width is made smaller, ±△ia also becomes smaller, and the average value Ia of ia becomes even more equal to Ir. Become.

In this case, the effective value of the instantaneous current value ia of the load matches its average value Ia.

Next, in the circuit system of FIG. 1a, filter LP.

The generation of sustained vibration due to resonance in CF will be explained.

If the average current Ia of the load (motor) is controlled to be constant, the load may be subject to constant current control and constant power control at the same time.

That is, this is a case where the time constant of load change is larger than the vibration period of the filter, 7·πv/LFCF.

For example, an electric car has a very large moment of inertia, and the load (
There are times when there is no change in the current and voltage on the motor side, but the current and voltage on the power supply side fluctuates sufficiently.

In the circuit of Figure 1a during this period, the capacitor CF
The power supply voltage Vs and the power supply current I corresponding to the voltage charged in
The following equation (1) holds true between s, load voltage Va, load current Ia, load resistance Ra, and current setting value Ir.

Note that chopper loss is ignored here, and it is assumed that there is no energy accumulation at all.

This power supply current Is indicates the average input current to the chopper A, and when it is partially differentiated with respect to the laminate source voltage (variable as it fluctuates) vS· of the equation (2), the following equation (3) is obtained.

Note that here Is varies as a function of Vs, and ■a・I
Since a, etc. are constant according to the above conditions, equation (3) holds true, and here Ys is the input admittance when the circuit of Fig. 1 a is viewed to the right from the input terminal of chopper A, and G
L is also its conductance.

Therefore, as is clear from equation (3), negative conductance occurs in the circuit system of FIG. 1a.

This AC component equivalent circuit is shown in the figure with the DC power supply short-circuited, where LF', C12 are a and LF in the figure,
Cfe is shown in parallel, GF represents the conductance resulting in loss of the filter, and the combined admittance Y of the circuit in the figure is expressed by the following equation (4).

It oscillates continuously with a number of angular circumferences.

In FIG. 1, Ir and ia in the signal system are signal voltages (or currents) proportional to Ir and ia in the main circuit, and do not have the same numerical values as Ir and ia in the main circuit.

It is also expressed as M in other figures.

In order to prevent the occurrence of the above-mentioned sustained oscillation, conventionally, for example, in Fig. 1a, a capacitor CF is set so that the current setting value Ir follows the fluctuation of the power supply voltage Vs, as shown in Fig. 2.
A voltage divider K is inserted in parallel with the voltage divider K, and its voltage dividing terminal is introduced into the comparator B, so that the current setting value Irf is expressed by the following equation (7).
shall be.

Here, k is a proportionality constant, and its value is variable depending on the partial pressure ratio of k.

From equations (1) to (3), the following equations (8) to (10) are obtained.

Therefore, the input admittance Ys to the chopper A is positive, and the above-mentioned sustained oscillation does not occur in the filters L, CF.
This is clear from the fact that 2Ra>0 for Gp+.

The load current Ia (average current) can be set by the value of "k" as shown in equation (8), but the drawback is that the setting cannot be determined accurately because the average value of Vs, that is, Es, generally fluctuates. I'm having problems.

The present invention eliminates the shortcomings of the conventional chopper control method, and in short, adds the chopper input terminal voltage to the input current setting to the comparator directly or indirectly via a DC blocking filter, and equivalently adds the chopper input terminal voltage to the input current setting to the comparator. The purpose of this invention is to provide a chopper control method that cancels out the negative conductance that occurs in the input and suppresses sustained vibrations due to the negative conductance that occurs on the power source side, and other objectives and features will become clear from the description below.

Hereinafter, the present invention will be explained in detail based on the embodiments shown in FIG. 3 and below.

FIG. 3a is a circuit diagram for explaining one embodiment of the present invention, and the same parts as in FIG. 1 are designated by the same reference numerals.

In Fig. 1a, C is a filter such as a bypass or bandpass that blocks the DC component of the chopper input voltage, that is, the power supply voltage Vs, D is an amplifier with an amplification degree of ', and E is the first setting current. By adding Ir1 and the second setting current Ir2 from this amplifier, the power supply current ■r(-Ir1+■
r2) into comparator B.

Therefore, the average current Ia of the load is expressed by the following equation (11).

Here, H(s)Vs indicates a power supply voltage value that does not include the DC component passed through filter C, and therefore no steady-state error occurs in the control of Ia.

That is, in steady operation, even if there is a voltage fluctuation in the power supply Es, 'H(s)Vs20' is obtained in equation (11), and the average current Ia of the load is compared by the comparator B only with the first set current Ir1. This is because it is chopper controlled.

Next, according to equations (1) and (11), the input current to chopper A, that is, the power supply current Is, becomes, and the numerical value changes Vs・Is and Vs
I rl , k' H(s) , which does not change by
Considering Ra, equation (12) can be partially differentiated on both sides iVs (it is clear that Is is a function of Vs), so partial differentiation yields the following equation (13), and the value of this equation is the chopper A
represents the input admittance of

That's what I'm saying.

As is clear from equation (13), this admittance Ys is the sum of negative conductance -0L and admittance Yc, and the equivalent circuit of FIG. 3a is shown in the same figure.

That is, in the same figure, GF is the already mentioned filter LF-CF.
Since this is the loss of conductance, this circuit resonates, that is, in order for sustained vibration to not occur, the frequency at which vibration may occur is ω.

(Formula (6)) At nearby frequencies It is sufficient if it holds true.

Here, Gc is the conductance of the atomic tances Yc.

In order for this equation (14) to hold true, it is preferable to appropriately select the value H(s) representing the characteristics of the filter C and the amplification degree of the amplifier, and this is obvious to those skilled in the art.

FIG. 4 is another embodiment to further clearly understand the present invention, and depending on one's imagination, it can be a concrete representation of the filter C1 amplifier D and adder E in FIG.

Therefore, to explain Fig. 4, the filter C consists of a capacitor C3 and a resistor R3, and its time constant T=C3R3(
Equation (15)) is obtained.

The first set current I rl in equation (11) is obtained from the DC power supply E r s resistors R2, R1, and Rs.

Here, S is a complex variable related to Laplace transform and is jω in the frequency domain.

Also, it corresponds to the proportionality constant of the set current Ir2 in Note 2.
It will be given at

Here, Rs is a resistance for detecting the load current 1a.

The conductance GL due to the load is expressed by the formula (13), (1
6) Given by.

Then, the time constant T of filter C is the filter (LP, CF
) due to the angular resonance frequency ω.

If the relationship is set so that it is sufficiently large compared to , then in equation (17), H(ω.

)=1 is obtained, and by substituting this into equation (13), the following equation (21) is obtained.

That is, the conductance GO of the admittance Yc is It is given by and is a positive conductance.

Even under the worst condition for the internal loss GF-0 of the filter, the total contactance of the filter (LP, C
No resonance node or sustained vibration occurs in F).

In FIG. 4, F indicates a chopper drive circuit that drives a chopper (indicated by a switch within the broken line A, but may be replaced by a thyrisk) based on the output from the comparator B.

Furthermore, since the current setting value and the load current are compared at the input end of the amplifier, the gain of the amplifier is not related to the current setting value, and the current ripple width changes depending on the gain.

Comparator B compares the output voltage of the amplifier with zero voltage.

Although the filter C in FIG. 4 is a bypass filter, it is of course possible to replace it with a bandpass filter, and in this case, the time constant 1-' is appropriately set so as to obtain a positive tuftance.

As described above, according to the present invention, in constant current control using a chopper, negative conductance vibration occurring in a filter on the power supply side can be suppressed without amplifying steady-state control errors.

A similar effect can also be achieved with constant voltage control.

[Brief explanation of drawings]

Figure 1a is a circuit diagram that implements a conventional chopper control method, Figure 1a is an equivalent circuit diagram of Figure a to explain the generation of negative conductance vibration, and Figure 2 is a circuit diagram that uses a conventional chopper control force method. FIG. 3a is a circuit diagram for realizing one embodiment of the present invention, the equivalent circuit diagram thereof, and FIG. 4 is a circuit diagram for realizing another embodiment of the present invention. FIG. A: Chopper, B...Comparator, C: Filter, D: Amplifier, E...-IP calculator.

Claims (1)

[Claims] 1. An LC filter is provided on the power source side, and a chopper is provided between the power source and the load, and a control output is provided to the chopper based on the load current and a main setting current that determines the control operation level of the chopper. In the DC chopper control force formula that controls the load at a constant current by deriving A direct current chopper control force type, characterized in that the chopper is controlled by a current obtained by calculating the force p of the main setting current and the sub-setting current. 2. The DC chopper control force formula according to claim 1, characterized in that the main setting current and the sub-setting current are calculated by force p at a predetermined ratio.